Ticket #28 - MOD operations with chained delete/add get back error 53 on backend config
    
    Bug Description:  If you try and delete/add a config attribute, an error 53 is returned.
    
    Fix Description:  Allow a delete of a config attribute if we add it back in the same mod set.
    
    https://fedorahosted.org/389/ticket/28
    
    Reviewed by: Noriko (Thanks!)