Integrated session module into sip_audio_session.py

darcs-hash:20090212114402-58103-e26efa6f9e348d9bc23824f512d5a2e7b99267e6
fix msrp scripts to use WaveFile instead of play_wav_file

* add play_wav_file function to GreenEngine. it blocks until the sound has finished
* made sip_send_file.py use GreenEngine.play_wav_file instead of sleeping of half a sec

darcs-hash:20090212120928-b2873-b9ec7c56b781e1ffdd723a08c2c1237d99b6e377