Utilize EntityManagerInterface

In my efforts to create a custom entity manager for my Symfony2 project, I've come down to an issue tied to this file.

I've created my custom entity manager using the decorator and such rather than extending the EntityManager class itself, which is frowned upon in the documentation.

So far, the only issue I have run into is this class. It is tied directly to the EntityManager class, when it would be sufficient to use the EntityManagerInterface interface instead.

By using EntityManagerInterface for the function arguments on "configure()" and "enableFilters()", the functionality shouldn't be affected, but allows for more entity manager implementations (like when using the EntityManagerDecorator) than just the core EntityManager.

(I submitted a pull request earlier, but ended up messing it up; I'm new to Git/GitHub and didn't fully know what I was doing.)