2005-01-17  Michael Natterer  <mitch@gimp.org>

	Allow to drop stuff onto empty layers, channels and paths dialogs
	to create new items:

	* app/widgets/gimpcontainertreeview.h (struct GimpContainerTreeView):
	added "gboolean dnd_drop_to_empty".

	* app/widgets/gimpcontainertreeview-dnd.c: if "dnd_drop_to_empty"
	is TRUE, dispatch drops to empty views and to the empty area below
	all items.

	* app/widgets/gimpitemtreeview.c (gimp_item_tree_view_init): set
	"dnd_drop_to_empty" to TRUE.

	* app/widgets/gimpitemtreeview.c
	* app/widgets/gimpchanneltreeview.c
	* app/widgets/gimpdrawabletreeview.c
	* app/widgets/gimplayertreeview.c
	* app/widgets/gimpvectorstreeview.c: made all drop functions work
	with "dest_viewable" being NULL and changed drop_possible()
	implementations accordingly. Cleaned up the whole DND code a bit.

	* app/widgets/gimplayertreeview.c: removed color and pattern
	drop code...

	* app/widgets/gimpdrawabletreeview.c: and added it here so colors
	and patterns can be dropped to the channels dialog too.