regexp: update comment on (*Regexp).Longest

Missed this review comment.

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/7229084
time: fix error message from Parse

Was incorrectly discarding the offending text in some cases.

Fixes issue 4493.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7277050
runtime/debug: add controls for garbage collector

Fixes issue 4090.

R=golang-dev, iant, bradfitz, dsymonds
CC=golang-dev
https://codereview.appspot.com/7229070