onal provisions, we refused to extend Gibbs to allow claims to be asserted against nondiverse parties when jurisdiction was based on diversity, see Owen Equipment & Erection Coll. Kroger, 437 U.S. 365, 98 S. Ct. 2396, 57 L. Ed. 2d 274 (1978), and we refused to extend Gibbs to authorize supplemental jurisdiction over claims t