Disallow RDN change and single-value bypass using setattr/addattr.
    
    When setting or adding an attribute wiht setatt/addattr check to
    see if there is a Param for the attribute and enforce the multi-value.
    If there is no Param check the LDAP schema for SINGLE-VALUE.
    
    Catch RDN mods and try to return a more reasonable error message.
    
    Ticket #230
    Ticket #246