window port interface change - add mbehavior flags to start_menu()

Provide a way to communicate additional behaviors and/or appearances
desired from NetHack window port menus.

This is foundation work for changes to follow at a future date.

src/dungeon.c

@@ -2128,7 +2128,7 @@ xchar *rdgn;
     winid win = create_nhwindow(NHW_MENU);
 
     if (bymenu) {
-        start_menu(win);
+        start_menu(win, MENU_BEHAVE_STANDARD);
         lchoices.idx = 0;
         lchoices.menuletter = 'a';
     }