Fixed sending continual video fast update commands if detect remote as sending continuous marker bits in video stream.

Made continuous marker bit detection a little less aggressive, require three consecutive markers on same time stamp instead of two.
Fixed media patch bypass mode passing across media commands, in particular video fast update, from sink back to source.
Fixed getting NAT flag into OpalRTPSession.
Fixed typo in media patch bypass mode passing across media commands.
Fixed correct handling of RTCP TMMBR command for bit rate control, thanks David Corrie
Added extra debugging for VP8 to try and track down "Bitstream not supported" error
Back port hack to make sure get a retry of authentication, but no more than a retry.
Error concelment (handling missing data) does not appear to work. Or we are not using it right. Either way disable it or we eventually get a Error 5 in vpx_codec_decode - Bitstream not supported by this decoder.