Cleans up a few other corner cases too.

R=ken2
CC=golang-dev
https://golang.org/cl/1592045

Cannot assume that g == m->curg at time of signal.
Must save actual g and restore.

Fixes flaky crashes with messages like

throw: malloc mlookup
throw: malloc/free - deadlock
throw: unwindstack on self
throw: free mlookup

(and probably others) when running cgo.

R=iant
CC=golang-dev
https://golang.org/cl/1648043

R=r
CC=golang-dev
https://golang.org/cl/1597044

R=golang-dev
CC=golang-dev
https://golang.org/cl/1641043

R=ken2
CC=golang-dev
https://golang.org/cl/1627042

There's only one Go object file per package now,
so there's no need to parse the metadata and merge
metadata from multiple files.  Just save the original
and use it as __.PKGDEF verbatim.

R=r
CC=golang-dev
https://golang.org/cl/1647042

R=ken2
CC=golang-dev
https://golang.org/cl/1597043

This avoids a crash when using cgo where glibc's malloc thinks
that it can use some of the memory following the symbol table.
This fails because the symbol table is mapped read-only, which
affects the whole page.

R=rsc
CC=golang-dev
https://golang.org/cl/1616042

R=rsc
CC=golang-dev
https://golang.org/cl/1381041

R=rsc
CC=golang-dev
https://golang.org/cl/1652041

R=r
CC=golang-dev
https://golang.org/cl/1615042

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/1555042

R=rsc
CC=golang-dev
https://golang.org/cl/1585041

R=r
CC=golang-dev
https://golang.org/cl/1649041

R=rsc
CC=golang-dev
https://golang.org/cl/1633042

Although technically incorrect, we want this in order to parse X.509
certificates where a wildcard hostname ("*.example.com") has been put
into a PrintableString.

Fixes #850.

R=rsc
CC=golang-dev
https://golang.org/cl/1615043

R=r
CC=golang-dev
https://golang.org/cl/1644042

R=r
CC=golang-dev
https://golang.org/cl/1599043

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/1636043

R=rsc
CC=golang-dev
https://golang.org/cl/1626043

R=rsc
CC=golang-dev
https://golang.org/cl/1644041

 * disallow surrogate pair runes.
 * diagnose impossible type assertions
 * eliminate another static buffer.
 * do not overflow lexbuf.
 * add -u flag to disable package unsafe.

R=ken2
CC=golang-dev
https://golang.org/cl/1619042

R=r
CC=golang-dev
https://golang.org/cl/1631041

* Code for assignment, conversions now mirrors spec.
* Changed some snprint -> smprint.
* Renamed runtime functions to separate
  interface conversions from type assertions:
  convT2I, assertI2T, etc.
* Correct checking of \U sequences.

Fixes #840.
Fixes #830.
Fixes #778.

R=ken2
CC=golang-dev
https://golang.org/cl/1303042

R=gri
CC=golang-dev
https://golang.org/cl/1620042

(remains of the semicolon conversion)

R=rsc
CC=golang-dev
https://golang.org/cl/1623041

R=rsc
CC=golang-dev
https://golang.org/cl/1621041

(caused certain files to not be idempotent under gofmt)

- corrected golden files for go/printer
- slightly simplified some code in nodes.go (no impact on formatting)
- these changes have no impact on gofmt output of .go files under src, misc

fallthrough statement considered harmful!

R=rsc
CC=golang-dev
https://golang.org/cl/1593042

R=gri
CC=golang-dev
https://golang.org/cl/1616041

R=r
CC=golang-dev
https://golang.org/cl/1614041

R=gri
CC=golang-dev
https://golang.org/cl/1612041

*T2 implements I2, but T2 does not.

R=gri
CC=golang-dev
https://golang.org/cl/1613041

Fixes #844.

R=ken2, rsc, ken3
CC=golang-dev
https://golang.org/cl/1593041

Fixes #827.

R=ken2
CC=golang-dev, rsc
https://golang.org/cl/1592041

R=r, rsc
CC=golang-dev
https://golang.org/cl/1590041

R=rsc
CC=golang-dev
https://golang.org/cl/1581041

Specifically:
- introduced notion of "underlying type"
- removed notion of type compatibility
- consolidated rules about assignment compatibility in
  assignment compatibility section
- be consistent with specyfing that nil is the value
  for uninitialized variables that can be nil (this
  was not specified clearly for pointers, functions, interfaces)
- added/fixed various related links throughout
- clarify language on conversions

R=rsc, r, iant, ken2
CC=golang-dev
https://golang.org/cl/1536041

R=rsc
CC=golang-dev
https://golang.org/cl/1514041

R=r
CC=golang-dev
https://golang.org/cl/1535041

R=r
CC=golang-dev
https://golang.org/cl/1539042