AssertCount on HHVM freezes

This is an issue I discovered in fabpot/php-cs-fixer repository. When I'm using `$this->assertCount(1, $iterator)` the scripts hangs for more than 10 minutes on HHVM... (I have not waited any longer than that)

[This PR on fabpot/php-cs-fixer](https://github.com/fabpot/PHP-CS-Fixer/pull/491/files) is a workaround for the issue. 

This PR does not solve the issue. The test I added is actually passing in HHVM... I want to get some understanding why the tests freezes in PHP-CS-Fixer on HHVM. 

I tried, but I could not reproduce the issue on the [Finder Component](https://github.com/symfony/finder). I don't know how to move forward or where the bug is...