thread_GOOS.c becomes os_GOOS.c.

signal_GOOS_GOARCH.c becomes os_GOOS_GOARCH.c,
but with non-GOARCH-specific code moved into os_GOOS.c.

The actual arch-specific signal handler moves into signal_GOARCH.c
to avoid per-GOOS duplication.

New files signal_GOOS_GOARCH.h provide macros for
accessing fields of the very system-specific signal info structs.

Lots moving, but nothing changing.
This is a preliminarly cleanup so I can work on the signal
handling code to fix some open issues without having to
make each change 13 times.

Tested on Linux and OS X, 386 and amd64.
Will fix Plan 9, Windows, and ARM after the fact if necessary.
(Plan 9 and Windows should be fine; ARM will probably have some typos.)

Net effect: -1081 lines of code.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/7565048

Fixes #3867.
Fixes #3307.

R=bradfitz, dvyukov
CC=golang-dev
https://golang.org/cl/7735044

Fixes #4850.

R=golang-dev, bradfitz, rsc
CC=golang-dev
https://golang.org/cl/7745044

vs tip:
BenchmarkTCP4OneShot                    172994        40485  -76.60%
BenchmarkTCP4OneShot-2                   96581        30028  -68.91%
BenchmarkTCP4OneShot-4                   52615        18454  -64.93%
BenchmarkTCP4OneShot-8                   26351        12289  -53.36%
BenchmarkTCP4OneShot-16                  12258        16093  +31.29%
BenchmarkTCP4OneShot-32                  13200        17045  +29.13%

BenchmarkTCP4OneShotTimeout             124814        42932  -65.60%
BenchmarkTCP4OneShotTimeout-2            99090        29040  -70.69%
BenchmarkTCP4OneShotTimeout-4            51860        18455  -64.41%
BenchmarkTCP4OneShotTimeout-8            26100        12073  -53.74%
BenchmarkTCP4OneShotTimeout-16           12198        16654  +36.53%
BenchmarkTCP4OneShotTimeout-32           13438        17143  +27.57%

BenchmarkTCP4Persistent                 115647         7782  -93.27%
BenchmarkTCP4Persistent-2                58024         4808  -91.71%
BenchmarkTCP4Persistent-4                24715         3674  -85.13%
BenchmarkTCP4Persistent-8                16431         2407  -85.35%
BenchmarkTCP4Persistent-16                2336         1875  -19.73%
BenchmarkTCP4Persistent-32                1689         1637   -3.08%

BenchmarkTCP4PersistentTimeout           79754         7859  -90.15%
BenchmarkTCP4PersistentTimeout-2         57708         5952  -89.69%
BenchmarkTCP4PersistentTimeout-4         26907         3823  -85.79%
BenchmarkTCP4PersistentTimeout-8         15036         2567  -82.93%
BenchmarkTCP4PersistentTimeout-16         2507         1903  -24.09%
BenchmarkTCP4PersistentTimeout-32         1717         1627   -5.24%

vs old scheduler:
benchmark                           old ns/op    new ns/op    delta
BenchmarkTCPOneShot                    192244        40485  -78.94%
BenchmarkTCPOneShot-2                   63835        30028  -52.96%
BenchmarkTCPOneShot-4                   35443        18454  -47.93%
BenchmarkTCPOneShot-8                   22140        12289  -44.49%
BenchmarkTCPOneShot-16                  16930        16093   -4.94%
BenchmarkTCPOneShot-32                  16719        17045   +1.95%

BenchmarkTCPOneShotTimeout             190495        42932  -77.46%
BenchmarkTCPOneShotTimeout-2            64828        29040  -55.20%
BenchmarkTCPOneShotTimeout-4            34591        18455  -46.65%
BenchmarkTCPOneShotTimeout-8            21989        12073  -45.10%
BenchmarkTCPOneShotTimeout-16           16848        16654   -1.15%
BenchmarkTCPOneShotTimeout-32           16796        17143   +2.07%

BenchmarkTCPPersistent                  81670         7782  -90.47%
BenchmarkTCPPersistent-2                26598         4808  -81.92%
BenchmarkTCPPersistent-4                15633         3674  -76.50%
BenchmarkTCPPersistent-8                18093         2407  -86.70%
BenchmarkTCPPersistent-16               17472         1875  -89.27%
BenchmarkTCPPersistent-32                7679         1637  -78.68%

BenchmarkTCPPersistentTimeout           83186         7859  -90.55%
BenchmarkTCPPersistentTimeout-2         26883         5952  -77.86%
BenchmarkTCPPersistentTimeout-4         15776         3823  -75.77%
BenchmarkTCPPersistentTimeout-8         18180         2567  -85.88%
BenchmarkTCPPersistentTimeout-16        17454         1903  -89.10%
BenchmarkTCPPersistentTimeout-32         7798         1627  -79.14%

R=golang-dev, iant, bradfitz, dave, rsc
CC=golang-dev
https://golang.org/cl/7579044

This is necessary to submit netpoll for linux,386 linux,amd64

R=golang-dev, bradfitz, rsc
CC=golang-dev
https://golang.org/cl/7470050

Otherwise startup problems can be difficult to debug.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/7522046

R=golang-dev
CC=golang-dev
https://golang.org/cl/7812043

R=golang-dev
CC=golang-dev
https://golang.org/cl/7529049

vs tip:
benchmark                           old ns/op    new ns/op    delta
BenchmarkTCP4Persistent                 67786        33175  -51.06%
BenchmarkTCP4Persistent-2               49085        31227  -36.38%
BenchmarkTCP4PersistentTimeout          69265        32565  -52.98%
BenchmarkTCP4PersistentTimeout-2        49217        32588  -33.79%

vs old scheduler:
benchmark                           old ns/op    new ns/op    delta
BenchmarkTCP4Persistent                 63517        33175  -47.77%
BenchmarkTCP4Persistent-2               54760        31227  -42.97%
BenchmarkTCP4PersistentTimeout          63234        32565  -48.50%
BenchmarkTCP4PersistentTimeout-2        56956        32588  -42.78%

R=golang-dev, bradfitz, devon.odell, mikioh.mikioh, iant, rsc
CC=golang-dev, pabuhr
https://golang.org/cl/7569043

The problem is that new network poller can have spurious
rediness notifications. This implementation ensures that
the socket is actually connected.

R=golang-dev, rsc, akumar
CC=golang-dev
https://golang.org/cl/7785043

An earlier CL disallowed ~ anywhere in GOPATH, to avoid
problems with GOPATH='~/home' instead of GOPATH=~/home.
But ~ is only special in the shell at the beginning of each of
the paths in the list, and some paths do have ~ in the middle.
So relax the requirement slightly.

Fixes #4140.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/7799045

Fixes #4235.

R=rsc, dave, r, dr.volker.dobler
CC=golang-dev
https://golang.org/cl/7438051

The new build tag "go1.1" will be satisfied by any Go 1.z release >= 1.1.
In general, the build tag "go1.x" will be satisfied by any Go 1.z release >= 1.x.
What happens when we reach Go 2 is yet to be decided.

The tags "go1" or "go1.0" are missing, because +build tags did not exist
before then, and also because the Go 1.0 releases do not recognize them.

The new -installsuffix flag gives access to the build context's InstallSuffix
(formerly named InstallTag, but not part of Go 1.0), for use in isolating
builds to custom directories. For example -race implies -installsuffix race,
and an AppEngine-specific build might use -tags appengine -installsuffix appengine.

Fixes #4116.
Fixes #4443.

R=golang-dev, bradfitz, r
CC=golang-dev
https://golang.org/cl/7794043

Eliminate false positives when you can tell even without
type information that the literal does not need field tags.

Far too noisy otherwise.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/7797043

Point the user to "go tool pprof" and mention some
important flags.

Fixes #4990.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7657045

valgrind complained that under some circumstances,

    *nr = *nc

was being called when nr and nc were the same *Node. The suggestion my Rémy was to introduce a tmp node to avoid the potential for aliasing in subnode.

R=remyoudompheng, minux.ma, rsc
CC=golang-dev
https://golang.org/cl/7780044

All the headings are CAPS not Title.

Fixes #4843.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7792043

If a fixed size array is passed in as the decode target and the JSON
to decode has extra array elements that are objects, then previously
the decoder would return a "data changing underfoot" error.

Fixes #3717.

R=golang-dev, adg, rsc
CC=golang-dev
https://golang.org/cl/7490046

Fixes #3838.

R=dave, mikioh.mikioh, rsc
CC=golang-dev
https://golang.org/cl/7511043

Also change prefix generation to use more human-friendly prefixes.

Fixes #5040.

R=golang-dev, r, bradfitz
CC=golang-dev
https://golang.org/cl/7777047

Just use "go tool addr2line" no matter what, since we know
it works for all OSs.

Fixes #4818.

R=rsc, r
CC=golang-dev
https://golang.org/cl/7526047

Fixes #4972.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7649044

Don't call unix-only function in test init.

R=golang-dev, alex.brainman
CC=golang-dev
https://golang.org/cl/7778043

Correctly indent the body of functions that have been declared
over multiple lines. See http://play.golang.org/p/MHMwNDbFyf for
an example.

Previously, the body of the function would be indented as deep as
the continuation line of the function declaration. Now it gets
indented as deep as the func keyword.

R=adonovan, cw, patrick.allen.higgins
CC=golang-dev
https://golang.org/cl/7628043

R=golang-dev, r, iant, iant
CC=golang-dev
https://golang.org/cl/6454072

On BSD variants, the tests need surely constructed IPv6
routing table.

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/7776043

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7480047

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/7529048

Fixes #4705.

Note that libjpeg will print a warning to stderr if there are many
extraneous bytes, but can be silent if the extraneous bytes can fit
into its int32 bit-buffer for Huffman decoding. I'm guessing that
this is why whatever encoder that produced the image filed for issue
4705 did not realize that they are, strictly speaking, generating an
invalid JPEG. That issue's attached image has two extraneous bytes.

For example, piping the program below into libjpeg's djpeg program
will print an "18 extraneous bytes" warning, even though N == 20.

$ cat main.go
package main

import (
        "bytes"
        "image"
        "image/color"
        "image/jpeg"
        "os"
)

const N = 20

func main() {
        // Encode a 1x1 red image.
        m := image.NewRGBA(image.Rect(0, 0, 1, 1))
        m.Set(0, 0, color.RGBA{255, 0, 0, 255})
        buf := new(bytes.Buffer)
        jpeg.Encode(buf, m, nil)
        b := buf.Bytes()
        // Strip the final "\xff\xd9" EOI marker.
        b = b[:len(b)-2]
        // Append N dummy 0x80 bytes to the SOS data.
        for i := 0; i < N; i++ {
                b = append(b, 0x80)
        }
        // Put back the "\xff\xd9" EOI marker.
        b = append(b, 0xff, 0xd9)
        os.Stdout.Write(b)
}
$ go run main.go | djpeg /dev/stdin > /tmp/foo.pnm
Corrupt JPEG data: 18 extraneous bytes before marker 0xd9

The resultant /tmp/foo.pnm is a perfectly good 1x1 red image.

R=r
CC=golang-dev
https://golang.org/cl/7750043

R=golang-dev, bradfitz, dave, rsc
CC=golang-dev
https://golang.org/cl/7547044

With the global redefinition of runtime·open by CL 7543043,
we need to provide a third argument and remove the cast
to the string.

Fixes build on 386 version of Plan 9.

R=khr, rsc, rminnich, ality
CC=golang-dev
https://golang.org/cl/7644047

Needed by TestResolveIPAddr. This makes us pass tests
again.

R=rsc, rminnich, ality, bradfitz
CC=golang-dev
https://golang.org/cl/7737043

Many thanks to Elias Naur for finding this with Valgrind on Linux.
Perhaps this is what is breaking the windows/amd64 builder.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/7595044

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7663045

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6727046

R=golang-dev, dave, iant
CC=golang-dev
https://golang.org/cl/7765043

The old description was misleading and inaccurate.

Fixes #4774.

R=iant, rsc, gri
CC=golang-dev
https://golang.org/cl/7761044

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7762046

See also https://golang.org/cl/7656044

R=golang-dev, gri, rsc
CC=golang-dev
https://golang.org/cl/7625048

Fixes #5033.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/7764044