don't include any gdk headers. added structure definitions for

don't include any gdk headers. added structure definitions for

Sat Sep  5 07:13:19 1998  Tim Janik  <timj@gtk.org>

        * gtk/gtktypeutils.h: don't include any gdk headers.
        added structure definitions for GtkTypeObject and GtkTypeClass,
        which cover the very basic fields of GtkObject and GtkObjectClass,
        which are actually used by the type system.

        * gtk/gtktypeutils.c: don't include gtkobject.h or gtkcontainer.h,
        we only refer to our own structures. improved class inheritance
        sanity checking a bit.

        * gtk/gtkobject.h: placed appropriate comments at the beginnings
        of the GtkObject and GtkObjectClass structures, which explain
        their relationship to GtkTypeObject and GtkTypeClass.

        * gtk/gtktypeutils.h:
        * gtk/gtkobject.h:
        moved GTK_STRUCT_OFFSET(), GTK_CHECK_CAST(), GTK_CHECK_CLASS_CAST(),
        GTK_CHECK_TYPE() and GTK_CHECK_CLASS_TYPE() macro definitions from
        gtkobject.h to gtktypeutils.h.

        * gtk/gtkobject.h:
        * gtk/gtkobject.c:
        removed gtk_object_check_cast() and gtk_object_check_class_cast()
        functions. to keep source compatibility, we can provide macro aliases
        for the corresponding gtk_type_* functions. but then again, people
        shouldn't have been using these functions anyways since they were part
        of Gtk's internal API.

        * gtk/gtktypeutils.h:
        * gtk/gtktypeutils.c:
        implemented gtk_type_check_object_cast() and gtk_type_check_class_cast()
        functions to check GtkTypeObject and GtkTypeClass types.