* app/paint_funcs.c:
	Fixed copy-on-write path of copy_region which was sometimes
	crashing with Scott's new tile scheme.

	* app/tile_manager.c:
	Added some sanity warnings.

	* app/xcf.c:
	Fixed copy-on-write tile loading which was causing crashes
	with Scott's new tile scheme.  Ref balance count seems funny
	still.