install freeglut for rosdep key glut on osx

I'm not 100% sure this is correct, but:
 * This key was last updated in 2012.
 * On Mavericks, I had to install freeglut in order to compile moveit_ros_perception, which depends on glut. Specific file/line that was problematic is https://github.com/ros-planning/moveit_ros/blob/indigo-devel/perception/mesh_filter/src/gl_renderer.cpp#L44
 * On Ubuntu (and all other linux distros), glut translates to freeglut.

@ahendrix @wjwwood Any thoughts?