net/http: support for setting trailers from a server Handler

We already had client support for trailers, but no way for a server to
set them short of hijacking the connection.

Fixes #7759

Change-Id: Ic83976437739ec6c1acad5f209ed45e501dbb93a
Reviewed-on: https://go-review.googlesource.com/2157
Reviewed-by: Andrew Gerrand <adg@golang.org>
doc: update links in FAQ

Vitess and protobuf has moved to GitHub; update the links.

Change-Id: I2d90bde1a7f2b590c8b7b08ce73d6faa13b51da0
Reviewed-on: https://go-review.googlesource.com/2166
Reviewed-by: Andrew Gerrand <adg@golang.org>
runtime: consolidate arch-specific signal handlers on Plan 9

Change-Id: I4379418853c523fc9aaeb5d6f37bc96117841418
Reviewed-on: https://go-review.googlesource.com/1786
Reviewed-by: David du Colombier <0intro@gmail.com>
Reviewed-by: Aram Hăvărneanu <aram@mgk.ro>
doc: add http server trailers support to go1.5.txt

Change-Id: Ic15e40bb1ae0bf3a4e8c43a44daf7cc35a18da87
Reviewed-on: https://go-review.googlesource.com/2192
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
archive/tar: document Reader.Next's behavior at the end

Change-Id: I72f6d0fc66dbee3f832d2d960b99a166a5bb10c3
Reviewed-on: https://go-review.googlesource.com/2191
Reviewed-by: David Symonds <dsymonds@golang.org>
go/parser: add {map,chan,interface} to expression lookahead tokens

+ tests that these parse:
  map[int]int{}[0]++
  interface{f()}(x).f()
  chan int(x) <- 0

Fixes #9474

Change-Id: If9fa57b3ab415ae7e93aa9935ec63edda8fe9d4f
Reviewed-on: https://go-review.googlesource.com/2178
Reviewed-by: Robert Griesemer <gri@golang.org>