Revision 57

	* Thuban/UI/view.py (MapCanvas.OnPaint): Only delay drawing to
	idle time when there actually is something to draw. If there's
	nothing to draw simply clear the window
	(MapCanvas.do_redraw): Call dc.EndDrawing and add some comments.
	(MapCanvas.SetMap): force a redraw in all cases because
	FitMapToWindow doesn't always do it.
	(MapCanvas.ZoomFactor): Add an optional parameter, center, to
	specify the point to move into the center of the window
	(ZoomOutTool.MouseUp, ZoomInTool.MouseUp): If the mouse wasn't
	dragged, zoon in/out by a factor of 2