fix Sensio FrameworkExtraBundle v3.0 ParamConverterInterface compatibility

Since Symfony 2.4 , required `sensio/framework-extra-bundle` version is >= 3.0.

But the `Sensio\Bundle\FrameworkExtraBundle\Request\ParamConverter\ParamConverterInterface` signature has changed (See `Request/ParamConverter/PropelParamConverter.php`).

Maybe we should create a 1.3 branch which require `symfony/symfony` >= 2.4  and `sensio/framework-extra-bundle version >= 3.0.