. . . "Since the early declaration in Barber v. Barber, 62 U.S. (21 How.) 582, 584, 16 L.Ed. 226 (1859), disclaim[ing] altogether any jurisdiction in the courts of the United States upon the subject of divorce, or for the allowance of alimony, federal courts have declined to assert diversity jurisdiction over actions for divorce, alimony, child support, child custody and other matters deemed to involve" .