PHPCR-107: Added support for sameNode as eqPath

http://www.doctrine-project.org/jira/browse/PHPCR-107

This PR makes the following possible:

````
$qb->($qb->expr()->orX(
    $qb->expr()->eqPath('/cms/content1'),
    $qb->expr()->eqPath('/cms/content2')
));
````

Which will allow us to fix the issue with batch delete in DoctrinePHPCRAdminBundle.

If all is OK will update documentation.