fix curved laser issue

This is a pull request that fixes the issue with the curved point cloud from the laser. It has been applied to simulator-gazebo on bitbucket before but it hasn't been applied here. The patch comes from Johannes :)

The old merge is here:
https://bitbucket.org/osrf/simulator_gazebo/pull-request/4/fixed-curved-laser-issue-thanks-johannes/diff 

Cheers,
Karol