fix bug in tick
fix bug in tick

Fixes issue 576.

R=rsc, rog
CC=golang-dev
http://codereview.appspot.com/196061

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go