Revision 122

	* Thuban/UI/view.py (MapCanvas): Derive from Publisher as well
	(MapCanvas.__del__): Implement because Publisher.__del__ has to be
	called.
	(MapCanvas.__init__): Bind EVT_LEAVE_WINDOW too. Initialize
	current_position
	(MapCanvas.set_current_position): New method to set
	current_position. Issue a VIEW_POSITION event
	(MapCanvas.CurrentPosition): New public method to return the value
	of current_position. Should be called when the VIEW_POSITION event
	is processed.
	(MapCanvas.OnLeftDown, MapCanvas.OnLeftUp, MapCanvas.OnMotion):
	Update the position.
	(MapCanvas.OnLeaveWindow): Set the position to None.