test/testlib: don't forget stderr for rundircmpout.
test/testlib: don't forget stderr for rundircmpout.

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/6620071

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