2004-01-14  Murray Cumming  <murrayc@usa.net>

        * gtk/src/treeiter.[hg}ccg]: Added TreeIter::set_stamp() and
        get_stamp(), with documentation, for use when implementing a
        custom TreeModel.
        * gtk/src/treemodel.[hg|ccg]:
        - Hand-coded several vfuncs and their C callbacks, so that we can have
        C++ iterators instead of GtkTreeIter*s in the API, and to reorder some
        parameters.
        - Added 2 extra vfuncs for information about root nodes. The C
        versions of these vfuncs provide root node information when the iter
        is NULL, but it is nicer in C++ to just have an extra vfunc without
        that parameter. This requires an extra if() in the _vfunc_callback()
        implementation.
        - Added documentation for the vfuncs but gmmproc does not yet put the
        documentation in the right place for the generated vfuncs.
        * gtk/src/cellrenderer.hg: Added docuemntation for the vfuncs, but
        gmmproc does not put this documentation in the right place yet.
        * examples/: Added treemodelcustom to show a derived TreeModel, which
        overrides those vfuncs, based on the example by Christof Pettig.