Sean Dunne's new documentary “Oxyana” was awarded a Special Jury Prize at the last Tribeca Film Festival, and it's easy to see why. Capitalizing on the current rage over oddball slice-of-life docs (see “The Queen of Versailles,”etc.), Dunne's straightforward portrait of a desolate West Virginia mining town ravaged by prescription drug abuse (Oceana, West Virginia, nicknamed “Oxyana” because of its Oxycontin problem) hits the right notes to ensure big indie success. He chooses a provocative topic, adeptly balances