Renamed _audio_transport attribute on Session to audio_transport

darcs-hash:20090217161314-58103-e77590f3bf61d86159bf5940d5b6eb1243337d29
Added folder to purge on un-install

darcs-hash:20090217193340-58252-440509b60cf6dbf70d3d007a08ce4b71cfa5de30