The snow was falling in Warsaw as David Bowie and Iggy Pop departed by train. Full to the brim with cheap sausages, having recently recovered their appetite after years of gorging on a purely nasal diet, they set off into the gloomy post-war city with a sense of artistic mystique abounding. They were in a bad way but recovering, and ideas were in bloom. The pair had never lost sight of music, even when they were having their swimming pools exorc…