Read the excerpt from "A Quilt of a Country."The New York of my children is no more Balkanized, probably less so, than the Philadelphia of my father, in which Jewish boys would walk several blocks out of their way to avoid the Irish divide of Chester Avenue. (I was the product of a mixed marriage, across barely bridgeable lines: an Italian girl, an Irish boy. How quaint it seems now, how incendiary then.) The Brooklyn of Francie Nolan's famous tree, the Newark of which Portnoy complained, even the uninflected WASP suburbs of Cheever's characters: they are ghettos, pure and simple. Do the Cambodians and the Mexicans in California coexist less easily today than did the Irish and Italians of Massachusetts a century ago? You know the answer.