exp/locale/collate: avoid double building in maketables.go.  Also added check.
exp/locale/collate: avoid double building in maketables.go.  Also added check.

R=r
CC=golang-dev
http://codereview.appspot.com/6202063
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go