cmd/go: make it work for code.google.com cloned repositories
cmd/go: make it work for code.google.com cloned repositories

Thanks to beatgammit for the fix.

Fixes issue 5408.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/13261048

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