Revision 159

	* Thuban/UI/view.py (PanTool.MouseMove): Use the bitmap the view
	maintains to redraw the window during a drag.
	(MapCanvas.unprojected_rect_around_point): New method to determine
	a small region around a point for hit-testing.
	(MapCanvas.find_shape_at): Only test the shapes in a small region
	around the point.