Fixes (legit) vet warnings.
Fix some verb tenses while we're here.

Updates #11041

Change-Id: I27e995f55b38f4cf584e97a67b8545e8247e83d6
Reviewed-on: https://go-review.googlesource.com/27122
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: David Crawshaw <crawshaw@golang.org>