net: use windows GetAddrInfoW in LookupPort when possible

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7252045
testing: SkipNow, FailNow must be called from test goroutine

Impossible for us to check (without sleazily reaching into the
runtime) but at least document it.

Fixes issue 3800.

R=golang-dev, bradfitz, dave
CC=golang-dev
https://codereview.appspot.com/7268043
reflect: explain StructField.Anonymous field as 'embedded'

The spec mostly uses the term embedded.
It's too late to change the field name but at least fix the docs.

Fixes issue 4514.

R=golang-dev, dave
CC=golang-dev
https://codereview.appspot.com/7235080
cmd/gc: clearer error for defer/go of conversion or invalid function call

Fixes issue 4654.

R=ken2
CC=golang-dev
https://codereview.appspot.com/7229072
cmd/gc: put 'not used' message on correct line

Fixes issue 4663.

R=ken2
CC=golang-dev
https://codereview.appspot.com/7235081
cmd/gc: silence redundant error prints for misuse of [...]int

Fixes issue 4452.

R=ken2
CC=golang-dev
https://codereview.appspot.com/7241065
cmd/gc: reject non-Go constants

Expressions involving nil, even if they can be evaluated
at compile time, do not count as Go constants and cannot
be used in const initializers.

Fixes issue 4673.
Fixes issue 4680.

R=ken2
CC=golang-dev
https://codereview.appspot.com/7278043
cmg/gc: Fix evaluation order of map indexing during multiple assignments

Fixes issue 4620.

R=rsc
CC=golang-dev
https://codereview.appspot.com/7241051