“Shackleton: The Biography” by Ranulph Fiennes; Pegasus Books (452 pages, $32) ——— Sometimes the greatest victories are hidden in defeats. Sir Ernest Shackleton wanted to be the first man to reach the South Pole, the first to cross Antarctica. He failed at both. Yet he became a hero anyway and is famous for his explorations. Ranulph Fiennes’ “Shackleton: The Biography” explains why. Part of an illustrious family (007′s current boss, Ralph Fiennes, is a cousin), Fiennes has been called the world’s greatest living explorer. Being a fellow arctic adventurer gives him “a unique perspective” on Sha…