cmd/vet: don't give error for Printf("%+5.2e", x)
cmd/vet: don't give error for Printf("%+5.2e", x)

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/5696048

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