First cut at tiled background images.

	There's no UI for setting them yet, they are only in
	the icon view, and they don't work properly with scrolling yet.

	* libnautilus/Makefile.am:
	* libnautilus/nautilus-gdk-extensions.c:
	* libnautilus/nautilus-gdk-extensions.h:
	* libnautilus/nautilus-gdk-pixbuf-extensions.c:
	* libnautilus/nautilus-gdk-pixbuf-extensions.h:
	Split the GdkPixbuf stuff into its own file.

	* libnautilus/nautilus-background.c:
	(nautilus_background_destroy): Fixed a bunch of leaks
	and added new code to stop pixbuf loading.
	(nautilus_background_draw): Added call to draw tiled
	background image. Converted gradients to use gdk_rgb
	instead of gdk_color.
	(nautilus_background_get_tile_image_uri): Implemented.
	(nautilus_background_set_color): Added short-circuit
	for background image case.
	(load_image_callback),
	(nautilus_background_set_tile_image_uri): Implemented.
	Include code to	load in the tiled image when its URI is set.
	(nautilus_background_receive_dropped_color): Set the
	tile image to NULL when a color is dropped.

	* libnautilus/nautilus-gdk-extensions.c:
	* libnautilus/nautilus-gdk-extensions.h:
	(nautilus_fill_rectangle_with_color),
	(nautilus_fill_rectangle_with_color),
	(nautilus_interpolate_color): Changed from gdk_color
	to gdk_rgb.
	(nautilus_parse_rgb_with_white_default): Added function
	for gdk_rgb similar to what we already have for gdk_color.

	* libnautilus/nautilus-icon-canvas-item.c:
	* libnautilus/nautilus-icon-container.c:
	* libnautilus/nautilus-list.c:
	Use gdk-pixbuf extensions in new location.

	* libnautilus/nautilus-metadata.h:
	Added metadata keys for background images.

	* src/ntl-view.c:
	Added lots of stronger checks for NAUTILUS_IS_VIEW since
	this is where we run into trouble with a bug I ran into.

	* src/file-manager/icon-view.c: Added code to handle
	the new background images.
	(create_icon_container): Keep around the handler ID when
	connecting to the "changed" message of the background so
	we can block the handler as needed.
	(fm_icon_view_begin_loading): Load the background image
	as well as the background color. We need to block the
	background changed signal handler so we don't get
	confused while the color but not the image is set up.
	(fm_icon_view_background_changed_callback): Save the
	background image URI as well as the background color in
	the metadata.