Supporters fear structure could be torn down as safety hazard and want it to become memorial to postwar foreign labourers in honour of its Turkish creator Sometimes the currents of history converge in a single spot. In Berlin, one of the most intriguing of those places is a small traffic island with a lovingly tended garden and a ramshackle two-storey structure called the Treehouse at the Wall. In 1983... [6567 chars]