Ticket 47767 - Nested tombstones become orphaned after purge
Bug Description: If there are nested tombstone entries, the parents will
always be purged first, which leaves its child entries orphaned.
Fix Description: When doing the tombstone purge, process the candidate list in
reverse order, which will remove the child entries before the
parent entries.
https://fedorahosted.org/389/ticket/47767
Reviewed by: nhosoi(Thanks!)