Recurrence: Broke out handleUntil as a separate function

- This means until porocesing is no longer controlled by rc.recurrence, which
  was never intended.

src/main.h

@@ -44,6 +44,7 @@ void updateRecurrenceMask (Task&);
 
 // recur2.cpp
 void handleRecurrence2 ();
+void handleUntil ();
 
 // nag.cpp
 bool nag (Task&);