* gdbtk-hooks.c (gdbtk_add_hooks): Set selected_frame_level_changed_hook

    * gdbtk-hooks.c (gdbtk_add_hooks): Set selected_frame_level_changed_hook
.
        (gdbtk_selected_frame_changed): New function.

        * gdbtk-cmds.c (Gdbtk_Init): Add command gdb_stack into interpreter.
        Link gdb's global selected_frame_level with interpreter global
        gdb_selected_frame_level.
        (gdb_stack): New function to faciltate speedier backtraces from
        gdbtk.
        (get_frame_name): New helper function for gdb_stack.