Added hold support in any state for Session

Ignore-this: f0dcf828bbbd9a77489e2e25943c68e3

darcs-hash:20090723091508-1e3d8-210d31b0607317f9daab00281617fb5300ed0b62
Modified sip_audio_session to use output device for tone ringing

Ignore-this: cbea6d8f7a06ae1e2d98618cd55bcd77

darcs-hash:20090723105819-1e3d8-be88229fce0ba34d77f6d222f1b8d21aa8e684d1