doc/go1.4.txt: add sync/atomic.Value
doc/go1.4.txt: add sync/atomic.Value

CC=golang-codereviews
https://codereview.appspot.com/145800043

tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go