Call it a comeback. Call it comeuppance. Call it checkmate. Call it what you will, but Tech. Sgt. Nathaniel Ola defeated Lt. Col. Douglass Taffinder and called it victory at the 2007 Air Force chess tournament held May 11 at Davis Monthan AFB, Ariz. Sergeant Ola, a missile warning duty officer assigned to the 614th Space Operations Squadron, is now