Ticket 47525 - Allow memberOf to use an alternate config area
    
    Description:  Added support for nsslapd-pluginConfigArea.  If this attribute is set
                  the config settings in the plugin entry are ignored, and only the
                  shared config entry will apply.
    
                  Registered a preop plugin function to perform config validation on
                  the shared config entry.  Then in the modify postop function we
                  apply the changes.
    
    https://fedorahosted.org/389/ticket/47525
    
    Reviewed by: richm(Thanks!)