Revision 1464

* Thuban/UI/messages.py (MAP_REPLACED): New message.

* Thuban/UI/viewport.py (ViewPort.SetMap): Issue MAP_REPLACED
after the new map has been assigned

* Thuban/UI/mainwindow.py (MainWindow.delegated_messages):
Delegate MAP_REPLACED to the canvas too
(MainWindow.prepare_new_session): Removed. Thanks to the new
MAP_REPLACED message it's no longer needed
(MainWindow.OpenSession, MainWindow.NewSession):
prepare_new_session has been removed.

* Thuban/UI/classifier.py (Classifier.__init__): Subscribe to
MAP_REPLACED so that we can close the dialog if a new map is set.
(Classifier.unsubscribe_messages): Unsubscribe from MAP_REPLACED
(Classifier.map_replaced): Handle MAP_REPLACED by closing the
dialog

* test/test_viewport.py (SimpleViewPortTest)
(SimpleViewPortTest.test_default_size): Add doc-strings
(ViewPortTest.setUp): Bind map to self.map so we can use it in
tests. Subscribe to MAP_REPLACED messages too.
(ViewPortTest.tearDown): No need to explicitly unsubscribe
(ViewPortTest.test_set_map): New test for the SetMap method.