runtime: precise garbage collection of hashmaps

R=golang-dev, rsc
CC=dave, dvyukov, golang-dev, minux.ma, remyoudompheng
https://codereview.appspot.com/7252047

Committer: Russ Cox <rsc@golang.org>
cmd/go: indicate that flags unrecognized by 'go test' must follow package specification

R=rsc, minux.ma
CC=golang-dev
https://codereview.appspot.com/7300063

Committer: Russ Cox <rsc@golang.org>