Plus automatic package<->project association script. (This is just a helper script for now. I intend to fully automate the associations further down the track.) R=rsc CC=golang-dev https://golang.org/cl/1715054
R=rsc, r, gri CC=golang-dev https://golang.org/cl/1476041
R=adg, r CC=cw, golang-dev https://golang.org/cl/224043