Folk artist Tom Russell brings his family saga to Tucson. By Gregory McNamee TRACING FAMILY HISTORY, genealogists will tell you, is an inexact science. It's not so much for lack of data: the world is afloat, after all, in birth and death certificates, deeds, snapshots, home movies. The challenge in uncovering one's roots is more often to separate fact from folklore, to cut through family politics, whitewashing (see Robert Altman's new film Cookie's Fortune for a case in point) and wishful thinking to find out what skeletons really lurk in Grandpa's closet. Singer-songwriter Tom Russell takes on his family history--folklore,