2006-09-26  Kristian Rietveld  <kris@imendio.com>

	* gtk/gtktreemodelsort.c (gtk_tree_model_sort_row_changed),
	(gtk_tree_model_sort_sort_level): ref count nodes the proper way,
	(gtk_tree_model_sort_ref_node), (gtk_tree_model_sort_real_unref_node),
	(gtk_tree_model_sort_free_level): bring zero ref count loops in
	sync,
	(gtk_tree_model_sort_free_level): free child levels before
	decreasing the zero ref count of the current level,
	(gtk_tree_model_sort_clear_cache): only clear cache if zero_ref_count
	is > 0.