[ZF2-273] Back out change to EventManager

- s/$listener/$listener->getCallback()/ -- fixes circular lookup issue
  that occurred.

src/EventManager.php

@@ -460,7 +460,7 @@ protected function triggerListeners($event, EventInterface $e, $callback = null)
         foreach ($listeners as $listener) {
             // Trigger the listener's callback, and push its result onto the
             // response collection
-            $responses->push(call_user_func($listener, $e));
+            $responses->push(call_user_func($listener->getCallback(), $e));
 
             // If the event was asked to stop propagating, do so
             if ($e->propagationIsStopped()) {