Historians are notorious for savaging historical fiction. We're quick to complain that writers project modern values onto their characters, get the surroundings wrong, cover up the seamy side of an era or exaggerate its evils — and usually, we're right. But AMC's hit show "Mad Men," which ends its fourth season next Sunday, is a stunning exception. Every historian I know loves the show; it is, quite simply, one of the most historically accurate television series ever produced. And despite the rampant chauvinism of virtually all its male characters (and some of its female ones), it is also one of the most sympathetic to women.