Ticket #410 - Referential integrity plug-in does not work when update interval is not zero
    
    https://fedorahosted.org/389/ticket/410
    Resolves: Ticket #410
    Bug Description: Referential integrity plug-in does not work when update interval is not zero
    Reviewed by: nhosoi (Thanks!)
    Branch: 389-ds-base-1.2.11
    Fix Description: Checking for newsuperior == NULL is not sufficient - also
    have to check for slapi_sdn_get_dn(newsuperior) == NULL as well.  Otherwise
    we write the string "(null)" to the referint log and that blows up the code
    that attempt to apply the change.
    Platforms tested: RHEL6 x86_64
    Flag Day: no
    Doc impact: no