A hundred-year mystery lured N.H. climber Mark Synnott into an unlikely expedition up Mount Everest. The mystery? On June 8, 1924, George Mallory and Sandy Irvine set out to stand on the "roof of the world," where no one had stood before. They were last seen eight hundred feet below the Everest summit. Did they summit decades before Sir Edmund Hillary and Tenzing Norgay in 1953? Irvine is believed to have carried a Kodak camera with him to record their attempt; could the frozen film reveal