"The process of gradual abolition in New England actually inscribed the practices of slavery itself in what was quite arbitrarily defined as the "free society" to which it gave birth. The fact that New Englanders began extolling their "free society" the minute the ink was dry on the gradual emancipation statutes does not mean that the statutes inaugurated a state of being that differed materially from the one that existed before the statutes were passed."