(Qmac_apple_event): Add extern.

(Qmac_apple_event): Add extern.
(set_frame_menubar, mac_menu_show keymp_panes)
(single_keymap_panes, list_of_panes, list_of_item)
(single_menu_item): Add argument types to prototypes.
(mac_dialog_show) [HAVE_DIALOGS]: Likewise.
(struct skp): New struct (from xmenu.c).
(single_keymap_panes, single_menu_item, list_of_panes)
(list_of_item): Sync with xmenu.c.
(Fx_popup_menu, Fx_popup_dialog): Likewise.  Don't get window from
POSITION if it is mac-apple-event event.
(menubar_selection_callback): Don't use menu_command_in_progress.
(set_frame_menubar): First parse all submenus, then make
widget_value trees from them.  Don't allocate any widget_value
objects until we are done with the parsing.
(parse_single_submenu, digest_single_submenu): New functions.
(single_submenu): Function deleted, replaced by those two.
(install_menu_quit_handler) [HAVE_CANCELMENUTRACKING]: Don't
create or dispose of EventHandlerUPP.  Install hander to all submenus.
(mac_menu_show) [!HAVE_MULTILINGUAL_MENU]: Use ENCODE_MENU_STRING
instead of ENCODE_SYSTEM.
(free_frame_menubar, fill_submenu, fill_menu): Don't use NULL for
integer values.
[HAVE_DIALOGS] (mac_dialog_show): Sync with xdialog_show (in xmenu.c).
(add_menu_item) [TARGET_API_MAC_CARBON]: Use CFString functions to
format menu item string.  Don't use NULL for integer value.