Revision 1344

Fixes RTbug #1974, 1971.
(MapCanvas.__init__): Subscribe to the idle time event. Set
        background color to white.
(MapCanvas.OnPaint): Set a flag indicating that we should
        render the map during idle time. If we already have a bitmap
        just draw it now.
(MapCanvas.OnIdle): New. Render the map only during idle time.
        This also fixes a problem with the busy cursor under gtk.