Added RootAudioBridge to skip not needed audio processing

Ignore-this: 48969a0c48f062adea179f3e5157c3f6

darcs-hash:20100419093843-1e3d8-fe6c680d592b99fe2ebfb3bb202aa58b6c77e92e
Broke circular reference between AudioStream and Session

Ignore-this: fbb8c01a869d432cec1f3c903963cb12

darcs-hash:20100419131717-1e3d8-0b0bc709c06dbb1431d34df77619d1ba7b36d72b