Introduce global stack segment cache and limit per-thread cache size.
This greatly reduces StackSys memory on workloads that create lots of threads.

benchmark                      old ns/op    new ns/op    delta
BenchmarkStackGrowth                 665          656   -1.35%
BenchmarkStackGrowth-2               333          328   -1.50%
BenchmarkStackGrowth-4               224          172  -23.21%
BenchmarkStackGrowth-8               124           91  -26.13%
BenchmarkStackGrowth-16               82           47  -41.94%
BenchmarkStackGrowth-32               73           40  -44.79%

BenchmarkStackGrowthDeep           97231        94391   -2.92%
BenchmarkStackGrowthDeep-2         47230        58562  +23.99%
BenchmarkStackGrowthDeep-4         24993        49356  +97.48%
BenchmarkStackGrowthDeep-8         15105        30072  +99.09%
BenchmarkStackGrowthDeep-16        10005        15623  +56.15%
BenchmarkStackGrowthDeep-32        12517        13069   +4.41%

TestStackMem#1,MB                  310          12       -96.13%
TestStackMem#2,MB                  296          14       -95.27%
TestStackMem#3,MB                  479          14       -97.08%

TestStackMem#1,sec                 3.22         2.26     -29.81%
TestStackMem#2,sec                 2.43         2.15     -11.52%
TestStackMem#3,sec                 2.50         2.38      -4.80%

R=sougou, no.smile.face, rsc
CC=golang-dev, msolomon
https://golang.org/cl/7029044

Update #4582.

R=nigeltao, dave, adg
CC=golang-dev
https://golang.org/cl/7070065

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7057064

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/7065067

Changeset f483bfe81114 moved ELF generation to the architecture
independent code and in doing so added a Section* to the Sym
type and an Elf64_Shdr* to the Section type.

This caused the Plan 9 compilers to complain about incompatible
type signatures in the many files that reference the Sym type.

R=rsc, dave
CC=golang-dev
https://golang.org/cl/7057058

Fixes #4186.

Back in the day, before the Go 1.0 release, $GOROOT was mandatory for building from source. Fast forward to now and $GOPATH is mandatory and $GOROOT is optional, and mainly used by those who use the binary distribution in uncommon places.

For example, most novices at least know about `sudo` as they would have used it to install the binary tarball into /usr/local. It is logical they would use the `sudo` hammer to `go get` other Go packages when faced with a permission error talking about the path they just had to use `sudo` on last time.

Even if they had read the documentation and set $GOPATH, go get will not work as expected as `sudo` masks most environment variables.

llucky(~) % ~/go/bin/go env | grep GOPATH
GOPATH="/home/dfc"
lucky(~) % sudo ~/go/bin/go env | grep GOPATH
GOPATH=""

This CL therefore proposes to remove support for using `go get` to download source into $GOROOT.

This CL also proposes an error when GOPATH=$GOROOT, as this is another place where new Go users can get stuck.

Further discussion: https://groups.google.com/d/topic/golang-nuts/VIg3fjHiHRI/discussion

R=rsc, adg, minux.ma
CC=golang-dev
https://golang.org/cl/6941058

R=golang-dev, bradfitz, minux.ma
CC=golang-dev
https://golang.org/cl/7057063

R=dave, golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7068044

The linker split PKGDEF into (prefix, name, def) pairs,
and defines def to begin after a space following the identifier.
This is totally wrong for the following export data:

        func "".FunctionName()
        var SomethingCompletelyUnrelated int

The linker would parse
    name=`"".FunctionName()\n\tvar`
    def=`SomethingCompletelyUnrelated int`
since there is no space after FunctionName.

R=minux.ma, rsc
CC=golang-dev
https://golang.org/cl/7068051

Our source no longer needs these flags set to build cleanly using clang.

Tested with

* Ubuntu clang version 3.0-6ubuntu3 (tags/RELEASE_30/final) (based on LLVM 3.0) on i386
* clang version 3.2 (tags/RELEASE_32/final) on amd64 cross compiling all platforms

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7058053

Fixes #4624.

R=rsc
CC=golang-dev
https://golang.org/cl/7058052

Fixes #4616.

R=rsc
CC=golang-dev
https://golang.org/cl/7069049

Fixes #4612.

R=rsc, iant, ken, r
CC=golang-dev
https://golang.org/cl/7076043

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/7063056

The old code made it impossible to implement a reverse proxy
with anything less than 4k write granularity to the backends.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/7060059

Fixes #4625.

R=iant, adg
CC=golang-dev
https://golang.org/cl/7064052

suggested by pkleiweg.

Fixes #3471.

R=adonovan, pkleiweg, rsc
CC=golang-dev
https://golang.org/cl/7060056

R=adonovan
CC=golang-dev
https://golang.org/cl/7060054

R=golang-dev, minux.ma
CC=golang-dev
https://golang.org/cl/7079043

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7061051

Fixes #4367.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7062052

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/7061050

Generated by addca.

R=gobot
CC=golang-dev
https://golang.org/cl/7064054

The spec talks explicitly about rune literals but the
respective production is still called char_lit for
historic reasons. Updated the two occurences.

Fixes #4602.

R=rsc, iant, r, ken
CC=golang-dev
https://golang.org/cl/7070048

A constant node of type uintptr with a nil literal could
happen in two cases: []int(nil)[1:] and
uintptr(unsafe.Pointer(nil)).

Fixes #4614.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7059043

There exists a test case for this condition, but it only runs on unix systems, which neatly dovetails into the code always using ':' as the list separator.

R=adg, iant
CC=golang-dev
https://golang.org/cl/7057052

Also adds a couple of simple tests for doc.Examples.

Fixes #4561.

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/7067048

ratio isn't 1x1.

Fixes #4259.

The test data was generated by
cjpeg -quality 50 -sample 2x2 video-005.gray.pgm > video-005.gray.q50.2x2.jpeg
cjpeg -quality 50 -sample 2x2 -progressive video-005.gray.pgm > video-005.gray.q50.2x2.progressive.jpeg

similarly to video-005.gray.q50.* from
http://code.google.com/p/go/source/detail?r=51f26e36ba98
the key difference being the "-sample 2x2".

R=rsc
CC=golang-dev
https://golang.org/cl/7069045

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7057051

There's no b in race detector.
The new flag matches the one in the go command
(go test -race math).

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/7072043

Fixes #4101.

R=dsymonds, rsc
CC=golang-dev
https://golang.org/cl/7065048

- Missing parenthesis
- Fix bad phrasing

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7063048

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7067047

R=rsc, adg
CC=golang-dev
https://golang.org/cl/7057049

Fixes #4487.

R=rsc
CC=golang-dev
https://golang.org/cl/7057048

R=golang-dev, bradfitz, gri
CC=golang-dev
https://golang.org/cl/7065046

Fixes #4601.

R=golang-dev, rsc, bradfitz, kardianos
CC=golang-dev
https://golang.org/cl/7033046

Replacing division-by-power-of-2 with right-shift is valid for
zero too.

R=gri
CC=golang-dev
https://golang.org/cl/7027049

This proposal updates the dashboard builder to avoid relying on the (soon to be removed) support for using go get to download to $GOROOT. The result is

WORKSPACE=$(the value of the -buildRoot flag / $BUILDER_NAME + hg revision)
GOROOT=$WORKSPACE/go
GOPATH=$WORKSPACE

Required for CL 6941058.

R=minux.ma, adg
CC=golang-dev
https://golang.org/cl/7034049

cmd/gofmt: Add error handling for ioutil.WriteFile.
bufio: Consistency, rename e to err.
image: Consistency, fix comment for asReader.

R=golang-dev, dave, minux.ma, adg
CC=golang-dev
https://golang.org/cl/7029056