most part, this should not break anyone's code. However, it's now
    possible/encouraged to use g_object_ref()/g_object_unref() and other
      GObject features with these GDK types. The converted types are:
        GdkWindow, GdkDrawable, GdkPixmap, GdkImage, GdkGC, GdkDragContext,
	  GdkColormap

	  - All drawables including pixmaps used to have a type tag, the
	    GdkWindowType enumeration, which included GDK_WINDOW_PIXMAP.
	      GdkWindowType is now a property of GdkWindow _only_, and there is
	        no GDK_WINDOW_PIXMAP. You can use the GDK_IS_PIXMAP() macro
to see
  if you have a pixmap, if you need to know that.

  - GtkStyle and GtkRcStyle are now subclasses of GObject as well.
    This breaks theme engines quite badly, but shouldn't affect most
      other code.

      - xthickness/ythickness have moved from GtkStyleClass to GtkStyle
        (from class to instance). This gives themes a bit more flexibility
	  and is generally more of the Right Thing. You can trivially fix
	    your code with s/style->klass->xthickness/style->xthickness/g and
	      same for ythickness.