reviewed by: John Harper

	* configure.in:
	* libnautilus-extensions/nautilus-background-canvas-group.c:
	(nautilus_background_canvas_group_initialize_common),
	(nautilus_background_canvas_group_initialize),
	(nautilus_background_canvas_group_supplant_root_class):
	* libnautilus-extensions/nautilus-background-canvas-group.h:
	* libnautilus-extensions/nautilus-background.c:
	(nautilus_background_set_up_canvas):
	Turned on dithering for canvases (aa mode). We no longer expose
	NautilusBackgroundCanvasGroupClass, in nautilus-background-canvas-
	group.h. Now we just provide an API to do the class change.