go/build: document blank line required after build constraints

Fixes issue 3539.

R=golang-dev, dave, adg
CC=golang-dev
https://codereview.appspot.com/7206049

Committer: Andrew Gerrand <adg@golang.org>
all: use t.Skip{,f}

Replace various t.Log{,f} ; return checks with t.Skip{,f}.

R=golang-dev, n13m3y3r, bradfitz, adg, mikioh.mikioh
CC=golang-dev
https://codereview.appspot.com/7193044
doc/go_spec: remove extra space, align tags, and change a tab to a space.

R=golang-dev, adg
CC=golang-dev
https://codereview.appspot.com/7198048

Committer: Andrew Gerrand <adg@golang.org>
runtime: increase stack limit in a test
Otherwise the test is flaky.
Fixes issue 4698.

R=golang-dev, iant
CC=golang-dev
https://codereview.appspot.com/7133071
go/types: add String() method to Type interface.

All implementations delegate to typeString.

Though I don't wish to exploit gri's absence to change
his code, this change is pretty low-risk and he assented to it
in the blue ink in the doc below [gophers only].
https://docs.google.com/a/google.com/document/d/1-DQ4fxlMDs9cYtnkKhAAehX6MArjOQyJsRXp-6kiJLA/edit#

R=iant, gri, gri
CC=golang-dev
https://codereview.appspot.com/7200046
go/types: expose types.IsIdentical, the Type equivalence relation.

This function is absolutely critical for clients such as
exp/ssa, and too complex for clients to duplicate.

As with CL 7200046, gri expressed in the doc below [gophers
only] before going on leave that he intended to expose such a
predicate, though his wording suggests as an interface method
of Type rather than a standalone function.  (My preference is
for binary methods to be standalone; see "On Binary Methods",
Kim Bruce, 1995).  In any case if he wishes to move it that's
easily accommodated by clients.

https://docs.google.com/a/google.com/document/d/1-DQ4fxlMDs9cYtnkKhAAehX6MArjOQyJsRXp-6kiJLA/edit#heading=h.k3bwja7xony9

R=iant, gri, iant
CC=golang-dev
https://codereview.appspot.com/7203051