[AC] Bug fix in menubar.el

A couple functions in menubar.el (add-menu-item-1, and delete-menu-item) assume that any operations on a top-level menu are operations on current-menubar, and so overwrite it, regardless of whether this menu was passed in as an argument. A test case: (progn (setq my-menu '(("File" "---"))) (add-submenu nil '("Edit" "Editting") nil my-menu) (delete-menu-item '("File") my-menu) (and (assoc "Edit" my-menu) (not (assoc "File" my-menu)))) This should return t; it removes one submenu and adds another. On a 21.5.34 system, however, it will return nil as both add-submenu and delete-menu-item will fail to operate on the local menu. (It won't in fact clobber the current menu; this example's safe.) I'm attaching a patch to fix this.