HE'S BAAAACK! Lars Von Trier's "The House that Jack Built" will be shown at the Cannes Festival this year, helping to deliver a shot in the arm, a mixture of adrenaline and steroids, to the official selection. Seven years ago, Von Trier was ejected from the Cannes Festival after fumbling his way, with devil-may-care indecency, through a Q&A with the press following the screening of his film "Melancholia." I hadn't attended