Depending on net/http means depending on cgo.
When the tree is in a shaky state it's nice to see sync/atomic
pass even if cgo or net causes broken binaries.
R=golang-dev, dave, r
CC=golang-dev
https://golang.org/cl/10753044
deferred block. This makes hangs in the waiting code less likely
if a goroutine exits abnormally.
R=golang-dev, minux.ma
CC=golang-dev
https://golang.org/cl/7306052