Support sending multiple OpenID AX values
    
    This allows us to send list a list of attribute values in a standard compliant
    method.
    We now process the number of requested values of any requested attribute,
    and only send up to the maximum requested number.
    
    Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>
    Reviewed-by: Pierre-Yves Chibon <pingou@pingoured.fr>