Fixed RTEL support

When using doctrine RTEL, we  define the target entity with an interface:

``` xml
        <many-to-one field="parent" target-entity="IR\Bundle\CategoryBundle\Model\CategoryInterface" inversed-by="children">
            <join-column name="parent_id" referenced-column-name="id" on-delete="CASCADE" />
            <gedmo:tree-parent />
            <gedmo:sortable-group />
        </many-to-one> 
```


``` yaml
# app/config/config.yml
doctrine:
    # ....
    orm:
        # ....
        resolve_target_entities:
            IR\Bundle\CategoryBundle\Model\CategoryInterface: Acme\CategoryBundle\Entity\Category
```

The condition will always fail since it checks if the following classes are equals:

`Acme\CategoryBundle\Entity\Category` and `IR\Bundle\CategoryBundle\Model\CategoryModel`