Ticket #326 - MemberOf plugin should work on all backends
    
    Bug Description:  By design the memberOf plugin would only look at the backend from
                      which the group belonged to.  This makes it impossible to maintain
                      users and groups from different suffixes.
    
    Fix Description:  First I added a new config setting in the plugin to turn this on
                      and off.  Then we just look at all the backends when searching.
    
    https://fedorahosted.org/389/ticket/326
    
    Reviewed by: ?