cmd/api: be more robust against OS deleting temp files

OS X in particular deletes tmp files (but not directories)
pretty reliably.

Ask hg whether the go.tools directory in tmp is good before
using it.

Fixes issue Rob and others were reporting, which I just hit
myself now.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/13084049
bytes: clarify Equal docs

== isn't defined on slices, so don't use it in docs.

R=golang-dev, iant
CC=golang-dev
https://codereview.appspot.com/12983045
syscall: update routing socket parser for NetBSD 6 and beyond

NetBSD 6 kernel and beyond require 64-bit aligned access to routing
facilities.

Fixes issue 6226.

R=golang-dev, bsiegert, bradfitz
CC=golang-dev
https://codereview.appspot.com/13170043
doc/go_faq.html: fix non-grammatical sentence
With my apologies.

R=golang-dev, alex.brainman
CC=golang-dev
https://codereview.appspot.com/12984045