runtime: handle timer overflow in tsleep

Make sure we never pass a timer into timerproc with
a negative duration since it will cause other timers
to never expire.

Fixes issue 5321.

R=golang-dev, minux.ma, remyoudompheng, mikioh.mikioh, r, bradfitz, rsc, dvyukov
CC=golang-dev
https://codereview.appspot.com/9035047

Committer: Russ Cox <rsc@golang.org>
cmd/gc: remove "send used as value" hint

This message was helpful for pre-Go 1 users updating to Go 1.
That time is past. Now the message is confusing because it
depends on knowing what pre-Go 1 looked like.

Update issue 4697.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/13335051
codereview: update use of promptchoice for Mercurial 2.7

Fixes issue 6186.

R=golang-dev, bradfitz, remyoudompheng, rsc
CC=golang-dev
https://codereview.appspot.com/13112043

Committer: Russ Cox <rsc@golang.org>