Revision 242

(ThubanApplication.create_session):
Extend the doc string.
(ThubanApplication.subscribe_session)
(ThubanApplication.unsubscribe_session): New methods to
subscribe/unsubscribe to/from session channels.
(ThubanApplication.SetSession): Call the new methods here.
(ThubanApplication.maps_changed, ThubanApplication.set_map):
Renamed set_map to maps_changed. Its now a subscriber for
MAPS_CHANGED.