The celebrity endorsements have begun! Savage Dragon, a superhero and police officer whose adventures are published by Image Comics, is throwing his hat in the ring for Barack Obama. The news is blared across the cover of issue No. 137, with the green-skinned hero dressed up for the occasion in a black jacket, crisp white shirt and striped red tie.The senator is also dressed nattily, though sartorial sticklers might point out that his tie falls a few inches too short. ("That's just because I'm an idiot," says Erik Larsen, who created the Savage Dragon character.) . . .