netchan: Avoid race condition in test.
netchan: Avoid race condition in test.

Make sure we export the channels before we try to import
them.

R=r
CC=golang-dev
http://codereview.appspot.com/4077046
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go