flag: replace fail with failf
flag: replace fail with failf

R=golang-dev, adg
CC=golang-dev
http://codereview.appspot.com/4254061

Committer: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang