(popup_activated_flag, submenu_id)

(popup_activated_flag, submenu_id)
(next_menubar_widget_id): Remove variables.
(initialize_frame_menubar): Remove function.
(pop_down_menu, mac_menu_show): Simplify save value.
(dispose_menus): New function.
(pop_down_menu, fill_menubar): Use it.
(fill_submenu): Remove function.  All uses changed to fill_menu.
(add_menu_item): Remove args SUBMENU and FORCE_DISABLE.  New arg
POS.  Don't call SetMenuItemHierarchicalID here.
(fill_menu): Add arg SUBMENU_ID.  Return submenu_id that is to be
used next.  Call SetMenuItemHierarchicalID here.
(fill_menubar): Add arg DEEP_P.  All uses changed.  Clean up menu
objects if needed.  Reuse existing menu bar titles if possible.
(set_frame_menubar): Don't clean up menu objects here.