Ticket 47640 - Linked attributes transaction not aborted when
     linked entry does not exit
    
    Bug Description:  When adding an entry and the target entry does not exist,
                      the operation is still allowed.
    
    Fix Description:  Return an error and useful error message to the client.
    
    https://fedorahosted.org/389/ticket/47640
    
    Reviewed by: nhosoi(Thanks!)