BostonSOME PARENTS probably had visions of incontinence on long family car trips when Alexandra Kerry promised Thursday night that, should her father become president, our children will be able to "control their own bodies." But if the reference went over the heads of confused Middle Americans, abortion advocates had no trouble recognizing it as a bone thrown their way by the Democratic campaign. Kerry's own challenge to President Bush--"Let's never misuse for political purposes the most precious document in American history, the Constitution of the United States"--will have been received in living rooms across the nation as an insistence that...