Sat Mar  7 20:20:53 1998  Tim Janik  <timj@gimp.org>

        * gtk/gtkobject.c:
        (gtk_object_check_cast):
        (gtk_object_check_class_cast):
        made the object/class cast checks much more descriptive, based on
        gtk-draco-980305-2.patch.gz and gtk-draco-980306-1.patch.gz but
        optimized for common code path.

        * gtk/gtkpreview.c: added a few extra checks for the visual
        (gtk-draco-980305-0.patch.gz).

        * gdk/gdk.c (gdk_signal): abort() on a signal if G_ENABLE_DEBUG
          is defined, so we dump core (gtk-draco-980305-0.patch.gz).