Bug 625014 - SubTree Renames: ModRDN operation fails and the server hangs if the entry is moved to "under" the same DN.
https://bugzilla.redhat.com/show_bug.cgi?id=625014
Description: adding a check if the newsuperior is the entry itself
or its descendent. If it is, modrdn returns LDAP_UNWILLING_TO_PERFORM.