If Ithaca has a twilight zone, it is Collegetown, particularly the back alleys of the remaining WW II-vintage tenement-like buildings along Stewart Avenue and College Avenue. When you enter an alley way it is 2006. But look up, now, it could just as well be 1986 or 1966 or 1946, the dim figures in the windows could be your parents, or your grandparents, for that matter. Listen: that’s Dave Matthews wafting out the window, or is that Linda Rondstadt? No, The Kingston Trio. Hey! That’s Perry Como. Doesn’t matter. You’re somewhere in Collegetown, and there’s no escape tonight…