mnet: changes to core moode libs

mnet: changes to core moode libs

 - get_user_listing() is now aware of remote users
 - require_login() is now aware of remote users
 - new auth plugins infrastructure in place
 - is_internal_auth() is now a deprecated legacy call
 - create_user_record()/update_user_record()/authenticate_user_login() handle multi-auth
 - is_mnet_remote_user() checks for remoteness
 - clean_param() handles PARAM_PEM and PARAM_BASE64

Also
 - user_login_string() knows to offer a link to remote users to login @ their host
 - XMLTDBTable field creation returns the field obj so that
   the caller has a chance to set additional properties such as comment