Find lwlib.h and xlwmenuP.h in ../lwlib.

Find lwlib.h and xlwmenuP.h in ../lwlib.

Reshuffle functions; put new ones in #ifdef USE_X_TOOLKIT.
(Fx_popup_menu): Add USE_X_TOOLKIT conditional around new decls.

(string_width): New function.
(event_is_in_menu_item, map_event_to_object): Likewise.
(set_menu_items, free_menu_items, popup_selection_callback): Likewise.
(popup_down_callback, free_menubar_widget_value_tree): Likewise.
(update_one_frame_psheets, set_frame_menubar): Likewise.
(Fx_popup_menu, xmenu_show): Handle USE_X_TOOLKIT.

(dispatch_dummy_expose): New function.
(XMenu_xpos, XMenu_ypos): Change the values of the constant assignment.
(xmenu_show): Change the way to make the menubar to redraw itself by
generating a dummy expose event.