McDonald's turned 50 this year. And, like many 50-year-olds, Ronald is in the thick of a midlife crisis. Yet, in contrast with the pencil-pushing, righteous-living ways of many who feel the urge to indulge their inner adolescents, McDonald's has gotten all the play out of the way. The Happy Meal lifestyle couldn't last forever, much as the joy that comes from shoving a Big Mac down your craw and following it with a haystack of fries turns inevitably bilious and dyspeptic. So now McDonald's is on a bit of a health kick, pushing salads and apple slices instead of slobbery...