MediaStreams

This gets the `streamtest` example working. The example shows forwarding MediaStreams for relay/broadcast scenarios.

Mostly I uncommented the MediaStream code that was already in there. I had to make some changes to get it to compile.

I also updated the example to show the original stream that is being sent and the stream that is being rebroadcast.

Enabling TRACING/debug shows that some things may not be cleaned up when a PeerConnection terminates.

Note: There are currently issues with libwebrtc preventing audio tracks from being properly forwarded. It might be possible to hack in a patch to get it working in this case, but according to the webrtc tracker it may be more difficult: https://code.google.com/p/webrtc/issues/detail?id=2192