Make catkin_install_python code a little clearer (#1054)
Make catkin_install_python code a little clearer (#1054)

* file -> source_file, rewritten_file

Signed-off-by: Shane Loretz <7fde345e8e2e22c78a1570a4807e4629866dc7de@osrfoundation.org>

* Add comments

Signed-off-by: Shane Loretz <7fde345e8e2e22c78a1570a4807e4629866dc7de@osrfoundation.org>

ros/catkin,ros/catkin,ros/catkin