Renamed SDPMedia to SDPMediaStream

Ignore-this: 863f0a206032f921597f4c65457a2ced

darcs-hash:20090622081846-1e3d8-3223e6e2cd8c4ec8d1e37eb8a39c6bcbbb7e0cf5
Fixed sip_audio_session to not fail if no stun servers found

Ignore-this: 5bc18d96073aba75c52f6d3a22464d0c

darcs-hash:20090623140904-1e3d8-86f1896c114461e141a51f42c744947a9d805f6b