Add WebRTC's FEC processing to ExternalOutput

WebRTC does FEC processing to reduce corruption in video due to packet loss.  Let's implement that!  I stripped out just the FEC portion of WebRTC and incorporated that.  One important note: WebRTC has its own endianness detection that's implemented in rtp_utility.cc; it is very important to get that right or you're find yourself exploding inside std::list in a really confusing way.  I think the routine as-is will work for licode across the board, but we probably want to double-check that.

Recording should be unaffected; the only consequence of this change should be "less corruption" in output video.  Corruption is still possible until ExternalOutput starts receiving retransmitted packets coming in on the Rtx SSRC channel.
Remove err.txt, accidentally checked in.
Merge pull request #189 from jnoring/upstream

Add WebRTC's FEC processing to ExternalOutput