Carla Bley, the wily and iconoclastic American composer, has a natural aversion to hearing other people interpret her music. But she didn't seem to have that problem with Riverside, a band jointly led by trumpeter Dave Douglas and multi-reedist Chet Doxas. In fact, she'll be joining Riverside, on piano, for a pair of upcoming Canadian concerts — in Quebec City on July 5 and at the Montreal Jazz Festival on July 6. Her receptivity to Riverside's album The New National Anthem, which celebrates her