The Berlin ExchangeA modern master at work THE TIMES Heart poundingly suspenseful WASHINGTON POST Joseph Kanon owns this corner of the literary landscape LEE CHILD Berlin, 1963. The height of the Cold War and an early morning spy swap. On one side of the trade: Martin Keller, an American physicist who once made headlines, but who then disappeared into the English prison system. Keller's most critical possession: his American passport. His most ardent desire: to see his