Bug 989 - Add a search path for clutter script assets

	* clutter/clutter-script.h:
	* clutter/clutter-script.c:
	(clutter_script_finalize),
	(clutter_script_add_search_paths),
	(clutter_script_lookup_filename): Add the ability to define multiple
	search paths inside ClutterScript and to look up a specific filename
	inside those search paths. This is useful to define a set of
	directories where the assets for a UI definition are and still
	reference those assets by their name instead of the full path. (989,
	based on a patch by Matthew Allum)

	* clutter/clutter-texture.c:
	(clutter_texture_set_custom_property): Use the newly added
	clutter_script_lookup_filename() function.