It's implemented as a separate constraint instead of adding properties
to the existing constraints.
Motors only apply linear and angular impulses and don't limit the
movement of rigid bodies, so it's best to use them in conjunction with
other constraints to limit the degrees of freedom.
Thanks to Markus Kasten (markus111) for the initial patch.
This modules does not depend on any blender-specific data
structures or algorithms and due to our policy better be
placed to intern/
Shall be no functional changes, tested CMake and SCons on
Linux, hopefully other platforms will work as well.
P.S. SVN history shall be preserved for the files.