Though it’s probably true that Christopher Nolan is a normal human being with guilty pleasures and intense feelings of love and hatred for silly things, there’s something about his mystique that makes people believe that the “Inception” filmmaker is uber-serious and only enjoys the finer things. But as revealed in a new oral history of “MacGruber,” Nolan has a soft spot for a film that features Will Forte prancing around with celery in his butt.