Delete hard references


The `deleteAllNodes()` method does not work as advertised if there are hard references anywhere inside of the repository. If someone is calling `deleteAllNodes()` it is likely that they are desiring that all of the nodes be deleted, references and all.

For example, `phpcr phpcr:purge` help states:

> The phpcr:purge command remove all the non-standard nodes from
> the content repository

This was not happening and an exception was thrown if references existed in the repository. I suppose it is possible that this was an implementation specific limitation.