'I got that song on my little laptop," Leonard Cohen says, sitting diminutively on a couch in his suite at the Warwick Hotel in Manhattan, both hands clutching an unsipped mug of coffee. He is discussing a new, unreleased track he's recorded, an accomplishment worthy of celebration for the notoriously slow-working Canadian singer, songwriter and recluse. "I should go get it. Want me to go get it?" He scampers out of the room and returns moments later with a black MacBook, opens iTunes and plays...