Revision 1782

(MainWindow.__init__): Subscribe to the
canvas' TITLE_CHANGED messages
(MainWindow.update_title): New. Update the main window's title
(MainWindow.__SetTitle): Removed. Use update_title instead.
(MainWindow.SetMap): Use update_title instead of __SetTitle
(MainWindow.RenameMap): Do change the window title explicitly
here. That's handled in a proper MVC way now.
(MainWindow.title_changed): New. Subscriber for the TITLE_CHANGED
messages