handle default sort feature

handle default sort feature

Mon Sep  3 18:03:56 2001  Jonathan Blandford  <jrb@redhat.com>

	* gtk/gtktreestore.c (gtk_tree_store_set_default_sort_func):
	handle default sort feature

	* gtk/gtktreesortable.c (gtk_tree_sortable_set_default_sort_func):
	new function to handle default sort.
	(gtk_tree_sortable_has_default_sort_func): check if default sort
	is set.

	* gtk/gtkliststore.c (gtk_list_store_set_default_sort_func):
	handle default sort feature