gofmt: race condition in error reporting and setting exit code

gofmt: race condition in error reporting and setting exit code

How to reproduce:

	$ mkdir /tmp/foo
	$ cp /dev/null /tmp/foo/bar.go
	$ chmod -r /tmp/foo/bar.go
	$ gofmt /tmp/foo
	open /tmp/foo/bar.go: permission denied
	$ echo $?		# should echo 2
	0
	$

Maybe you need to put a call to time.Sleep at the beginning of report().

R=gri
CC=golang-dev
https://golang.org/cl/164073