Ticket 48197 - error texts from preop plugins not sent to client
    
    Bug Description: SLAPI_PLUGIN_BE_PRE_MODIFY_FN failed operations do not
                     retrieve the error text in ldbm_modify.c
    
    Fix Description: Get the error text when we receive an error.
    
    https://fedorahosted.org/389/ticket/48197
    
    Reviewed by: lkrispenz(Thanks!)