A sleeper hit at the Tribeca Film Festival (which really should be called the Chelsea-East Village FF, because that’s where most of the movies screen) is “Magic Valley,” an American film with European sensibilities by neophyte director Jaffe Zinn. Set in Buhl, Idaho, it takes three seemingly unrelated stories and weaves them together into a disturbing portrait of small-town life.  The movie was warmly received when it was shown Saturday afternoon. One more screening remains, Wednesday at 6:45 p.m. at the Chelsea Cinema.