From Clint Longley in the clutch to Leon Lett in the snow, the Cowboys on Thanksgiving is always a traditional, appetizing feast. New helmets. Old friends. Older foes. The Jones family, the Jonas Brothers, the New York Giants, the Salvation Army and all the other familiar Thanksgiving trimmings centered around – not turkey – but the Dallas Cowboys. When the Cowboys host their division-rival Giants Thursday afternoon at AT&T Stadium, it will be both a chance to shoot up the NFC standings and to savor one of the richest, most iconic traditions in American sports. For all but two years…