test/run: clear $E in case it's already set in environment.
test/run: clear $E in case it's already set in environment.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4312054
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go