Removed the use of ToneGenerator in sip_audio_session

Ignore-this: b36b51c37135ef062b6a3a39c54b7185

darcs-hash:20091204095617-1e3d8-dbdefd57aeae77748452e19f2a20f581afe13391
Added inband DTMF-playing to sip_audio_session

Ignore-this: 1cd1fb6376eab45208a420d34458e228

darcs-hash:20091204152346-1e3d8-28e71f7bd7b601ada807792d3e66e49b2d4ed075