fix a few places where I was confused between modelsort iters and other

fix a few places where I was confused between modelsort iters and other

Thu Dec 27 16:37:04 2001  Kristian Rietveld  <kris@gtk.org>

        * gtk/gtktreemodelsort.c (gtk_tree_model_sort_row_deleted),
        (gtk_tree_model_sort_sort_level),
        (gtk_tree_model_sort_insert_value): fix a few places where
        I was confused between modelsort iters and other iters. This was
        really going to happen someday ;)