Bug 735114 - renaming a managed entry does not update mepmanagedby
    
    When a number of different plug-ins are being used that perform
    internal operations to update entries, it is possible for the
    managed entry plug-in to fail to update the managed entry.  In
    particular, it has been found that renaming an origin entry can
    trigger a plug-in other than the managed entry plug-in to rename
    the managed entry.  This causes the managed entry plug-in to fail
    when it attempts to update the managed entry.
    
    This patch makes the managed entry plug-in check if the managed
    entry has already been renamed when processing a MODRDN operation.
    If it detects that the managed entry has already been renamed, it
    will use the new DN to perform the managed entry updates.