An inexplicably compelling, far-outside-the-box excursion from director Gus Van Sant, “Gerry” is a modestly sweeping experimental movie — one of very long takes and very little dialogue — about little more than two buddies getting lost in the desert.”Gerry” is not a movie about dramatic subjects like survival (no mention is made of hunger) or self-discovery. Nor is it about ostentatious acting challenges. But it is a meditative, metaphorical, metaphysical, largely internalized exploration of friendship and personal tribulation. And it’s a welcome return of Van Sant to his roots as one of American cinema’s more daring filmmakers.