sync: improve WaitGroup example by putting the call to Done in a deferred block. This makes hangs in the waiting code less likely if a goroutine exits abnormally.
sync: improve WaitGroup example by putting the call to Done in a
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://codereview.appspot.com/7306052

Committer: Shenghou Ma <b563c57947dc20eb81988e3e3c22786764c14ca8@gmail.com>

apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,tv42/old-go,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,apparentlymart/golang,tv42/old-go,dsriram/golang,tv42/old-go,apparentlymart/golang,dsriram/golang,dsriram/golang,dsriram/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,gnanderson/go,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,gnanderson/go,dsriram/golang,tv42/old-go,gnanderson/go,dsriram/golang,tv42/old-go,dsriram/golang,apparentlymart/golang,pombredanne/go-deleteme