gofmt: gofmt test harness bug fix
gofmt: gofmt test harness bug fix

Don't use the rewrite rule from a previous test
for the next test if there is no rewrite rule
provided.

R=r, r2
CC=golang-dev
http://codereview.appspot.com/4419045

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go