Ticket 47525 - Crash if setting invalid plugin config area for MemberOf Plugin
Bug Description: Setting the nsslapd-pluginconfigarea to an entry that
does not have the required config attributes causes a
crash.
Fix Description: The plugin entry was being accidentally freed instead
of the config area entry.
The shared config area validation was being performed
in postop - this has now been moved into the preop stage.
Also, set the returntext when an error occurs.
https://fedorahosted.org/389/ticket/47525
Reviewed by: rmeggins(Thanks!)
(cherry picked from commit 42f935ab7406802d522f357048db1e68d729d5e5)