codereview: give advice on 'cannot create CL outside default branch'
codereview: give advice on 'cannot create CL outside default branch'

Fixes issue 3430.

R=golang-dev, bradfitz
CC=golang-dev
http://codereview.appspot.com/5981047
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go