nsfns.m (EmacsDialogPanel-runDialogAt): Add declaration of

timer_check() to avoid crash on Leopard/PPC.  Bug #2154.

src/nsmenu.m

@@ -1887,6 +1887,7 @@ void process_dialog (id window, Lisp_Object list)
 - (Lisp_Object)runDialogAt: (NSPoint)p
 {
   int ret;
+  extern EMACS_TIME timer_check (int do_it_now); /* TODO: add to a header */
 
   /* initiate a session that will be ended by pop_down_menu */
   popupSession = [NSApp beginModalSessionForWindow: self];