Associated Press: If federal renewable fuel mandates require ethanol to be mixed into gasoline, the nation’s largest independent oil refiner figures it might as well just do it itself. The ethanol industry is under duress partly due to overcapacity and biorefineries can now be had for pennies on the dollar. Valero Energy Corp. became the first conventional energy company to test the waters last week, bidding $280 million for five ethanol plants owned by VeraSun Energy Corp., which is now under …