Bug 675265 - preventryusn gets added to entries on a failed delete
    
    https://bugzilla.redhat.com/show_bug.cgi?id=675265
    
    Description: When an entry is deleted with Entry USN plugin enabled,
    an operational attribute preventryusn is added to handle indexes and
    entryusn tombstone.  The attribute must have been added only when
    the delete was successful, but it was added regardless of the result
    from the operation.  This patch checks the delete result in the
    newly added entryusn delete bepost plugin (usn_bepostop_delete).
    If it is not successful, the bepost plugin cleans up the attribute.