Ticket 47771 - Performing deletes during tombstone purging results in operation errors
Bug Description: An operations error can occur when deleting entry while
tombstone purging is happening. The error occurs when it
tries the lock the parent entry, but the parent entry was
replaced in the cache before it could be locked.
Fix Description: Return a special error code when cache_lock_entry fails because
the entry was marked as deleted. Then try to grab the entry
again and lock it.
Reviewed by: rmeggins & nhosoi(Thanks!!)