codereview: explain how to get hgpatch in error message
codereview: explain how to get hgpatch in error message

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/5623045

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