Fixed @throws hint

`\LogicException => \PHPCR\RepositoryException`

It's a real BC break but only in docblock.
What about introduce `UnauthenticatedException`?
i think we should remove this line entirely. it makes no sense to treat this method different than the rest. all operations need you to be logged in. otherwise we could copy-paste this to all methods that require a login, which is basically just all methods of this interface.