Use threading.RLock instead of thread.allocate_lock() in AudioStream

darcs-hash:20090427132818-58103-35e849e16705893a99614e76bf26725535ea4ee6
Added extra NULL pointer check in AudioTransport.start()

darcs-hash:20090427135852-58103-0b1982b882115fd62313cceee1b8286ce862a85d