Respect tf_prefix when sending maps
Fixed test files to use the new rosbag command layout.
Merge branch 'master' of github.com:felix-kolbe/slam_gmapping
Changed reference frame from base to laser to account for upside down and/or back facing laserscanners.

- Added a check if the scanner is facing down
- Added a safety check if the scanner is aligned planar
- Made laserscan min- and max-angles global as they are needed later for scanners with a negative angle-increment
- Replaced the base->laser pose for gmapping with the identity transform and included the base->laser part into the gmap_pose
- Removed a transform-lookup from the map->odom transformation process as it is not needed anymore

These changes should make gmapping more robust against laserscanners that are mounted upside down, facing backwards or are rotating counter-clockwise.
It will also allow gmapping to work with panning laserscanners, since the transform base->laser is no longer considered fixed.