Revision 2446

Alternative Path feature:
	* test/test_load.py (TestAltPath): New, tests for alternative path feature
	in load_session()
	(Shapefile_CallBack): Helper, implements controllable callback.

	* Thuban/UI/application.py (ThubanApplication.OnInit):
	Added "alt_path" to self.path
	(ThubanApplication.OpenSession): Added shapefile_callback as second
	callback similar to db_connection_callback.
	(ThubanApplication.run_alt_path_dialog): New, implementaion of
	shapefile_callback. In addition to raising the dialog the control of
	self.path('alt_path') is implemented here.

	* Thuban/Model/load.py (SessionLoader.__init__): Added shapefile_callback.
	(SessionLoader.open_shapefile): Open shapefile, eventually with
	alternative path. This wrapps the "theSession.OpenShapefile(filename)"
	formerly used in start_fileshapesource()/start_layer().
	(SessionLoader.start_fileshapesource): Call open_shapefile().
	(SessionLoader.start_layer): Call open_shapefile().
	(load_session): Added shapefile_callback.

	* Thuban/UI/altpathdialog.py: New, implements dialogs for alternative path
	feature (search / check).