“Oz the Great and Powerful” (PG, 130 minutes, Disney): Oscar Diggs (James Franco) is a sideshow conjurer with a traveling circus in 1905 Kansas, captured in the black-and-white, square-framed format of old-timey cinema. He’s forced to make a quick escape from the midway via hot-air balloon, at which point he’s caught in a cyclone that plops him down in a brightly colored, wide-screen world. If …