big: Rat test improvements
big: Rat test improvements

R=gri
CC=golang-dev
http://codereview.appspot.com/1270041

Committer: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go