go/build: fix some comments
go/build: fix some comments

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/6217044

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go