EventManager or Stdlib\CallbackHandler can't handle WeakRef enough.

In develop branch,
I got this error.

```
$ php -d extension=weakref.so /usr/bin/phpunit ZendTest/EventManager
PHPUnit 3.7.14 by Sebastian Bergmann.

Configuration read from /home/sasezaki/zf2/tests/phpunit.xml.dist

.....................................E........................... 65 / 86 ( 75%)
.....................

Time: 0 seconds, Memory: 3.25Mb

There was 1 error:

1) ZendTest\EventManager\EventManagerTest::testWeakRefsAreHonoredWhenTriggering
call_user_func() expects parameter 1 to be a valid callback, no array or string given

/home/sasezaki/zf2/library/Zend/EventManager/EventManager.php:460
/home/sasezaki/zf2/library/Zend/EventManager/EventManager.php:204
/home/sasezaki/zf2/tests/ZendTest/EventManager/EventManagerTest.php:560

FAILURES!
Tests: 86, Assertions: 224, Errors: 1.
```

I did run under environment.
```
$ php -v
PHP 5.4.11-1~precise+1 (cli) (built: Jan 24 2013 15:22:16) 
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2013 Zend Technologies
    with Xdebug v2.2.1, Copyright (c) 2002-2012, by Derick Rethans
```
(When turn off xdebug or -d apc.enabled=0, I got same error).


This WeakRef issue occurs ZendSkeletonApplication can't run.