Trac Ticket #494 - slapd entered to infinite loop during new index addition
    
    https://fedorahosted.org/389/ticket/494
    
    Bug Description: An entry which rdn is nsuniqueid=...,nsuniqueid=...
    was accidentally generated.  It broke the entryrdn tree and put
    the reindex and export into the the infinite loop.
    
    Fix Description: Added an missing check if the retrieved entry is
    already an tombstone or not.  This tombstone is the one converted
    by the entryusn plugin.  Please note that replication has an urp
    code which handles such conflicts.
    (cherry-picked from commit b963576d2758d29e8d21297e8f763d0373895b9f)
    (cherry picked from commit 31d15788d4e988646a42252f6ea351f033206a96)