Refuse or strongly warn when releasing package with capital letters

[wjwwood]

See: ros-infrastructure/bloom#191

Soon, bloom will refuse to release repositories with packages which have capital letters in the names, because it violates the ROS naming guidelines and more importantly the Debian guidelines. I considered that we could automatically lowercase the names, but then we might run into problems on systems without case sensitive filesystems.

I think it would be nice for catkin_prepare_release to catch this so people have a chance to repair the problem before tagging and running bloom, i.e. bloom is often too late for catching this. This would be further than the warning users get from catkin_pkg, because it will tell them that because of this naming problem bloom will refuse to release the repository.