This documentary, written and directed by Alex Gibney, may not be the boldest and bravest TV offering ever to probe, recount and question the basic tenets of Scientology (that distinction, believe it or not, still goes to an episode of South Park), but it’s close. In this potent two-hour study, Gibney’s strongest and most memorable segments involve one of two factors: new interviews with former Scientologists, including Oscar-winning screenwriter Paul Haggis, and vintage interviews,