Big Bird Tells All, Ruffles FeathersApril 29, 2003STEPHEN M. SILVERMANNot surprisingly, Big Bird has a big mouth. Actually, it's the man behind the "Sesame Street" Bird -- Caroll Spinney, 69, who's been the overgrown fine, yellow-feathered friend for the past 34 years on the children's show, which is an institution on PBS. Now, Spinney's autobiography, "The Wisdom of Big Bird," is hitting book stores Tuesday. It's anything but feather-brained, and Spinney -- sensitive to what his young fans might think -- is entering the tell-all arena carefully. "For years I've kind of hidden from the public because I've seen disappointed...