Tests for deleting same name siblings

As discussed in the last part of [this mailing list post](https://groups.google.com/d/msg/symfony-cmf-devs/Ro12vnxInG8/gj94zMoHuoIJ):

I've added some fixtures that use same name siblings (SNS). These would break jackalope-doctrine-dbal (even if I included uuid) so I created a separate test class with its own fixtures.