Changed set_channel_ids to restart the data thread. DemultiplexCatcher now has default channel_ids for testing. Coordinator's start_data_thread method could easily be altered to take channel arguments by calling set_channel_ids rather than start_data_thread (since set_channel_ids now calls start_data_thread). (reverse-merged from commit 129fc0107c235e38470215913e737ebabac37f54)