Added test to sip_audio_session.py to see if a failed session was because of a missing ACK and display that if it is

darcs-hash:20090116164143-58103-c750aba6a8782373ce2f701b226dd5e7edbe1ba1
Added high-level Session class, only supports audio without re-INVITEs

darcs-hash:20090116175020-58103-4166e30ab8cd9ffba55787fa8ba5b0278f06bcff