gofmt: use os.Stdin instead of opening /dev/stdin
gofmt: use os.Stdin instead of opening /dev/stdin

Opening /dev/stdin can sometimes fail. For example, in the acme editor,
executing "Edit ,|gofmt" fails with:

	open /dev/stdin: no such device or address

Executing "Edit ,|ls -l /dev/stdin /proc/self/fd/0" gives:

	lrwxrwxrwx 1 root root  15 2009-09-07 02:17 /dev/stdin -> /proc/self/fd/0
	lrwx------ 1 fhs  users 64 2009-11-26 22:05 /proc/self/fd/0 -> socket:[5528230]


(This is my first change, and I've signed the individual contributor license agreement.)

R=rsc, gri
CC=golang-dev
http://codereview.appspot.com/162041

Committer: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

h8liu/golang,bdwalton/debian-golang,bdwalton/debian-golang,h8liu/golang,bdwalton/debian-golang,tianon/debian-golang,ssrl/go,apparentlymart/golang,nightlyone/golang,pombredanne/go-deleteme,ssrl/go,ssrl/go,tianon/debian-golang,nightlyone/golang,ssrl/go,tianon/debian-golang,ssrl/go,bdwalton/debian-golang,gnanderson/go,nightlyone/golang,tianon/debian-golang,nightlyone/golang,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,bdwalton/debian-golang,apparentlymart/golang,ssrl/go,pombredanne/go-deleteme,dsriram/golang,h8liu/golang,bdwalton/debian-golang,nightlyone/golang,ssrl/go,h8liu/golang,dsriram/golang,bdwalton/debian-golang,dsriram/golang,nightlyone/golang,pombredanne/go-deleteme,apparentlymart/golang,tianon/debian-golang,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme,tianon/debian-golang,gnanderson/go,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,dsriram/golang,h8liu/golang,nightlyone/golang,gnanderson/go,gnanderson/go,dsriram/golang,tianon/debian-golang,apparentlymart/golang,gnanderson/go,gnanderson/go,h8liu/golang,tv42/old-go,apparentlymart/golang,tianon/debian-golang,tv42/old-go,bdwalton/debian-golang,tv42/old-go,h8liu/golang,apparentlymart/golang,gnanderson/go