Re-organise code so it can be applied on earlier version of SVN (from 20405) as well as latest (20450)

Modified AV-Sync code to fix a problem described in this thread.

It should help when the following condition occurs:

"Audio 686 ms behind video but already 75 video frames queued. AV-Sync might be broken. "

http://www.avenard.org/files/media/vdpau/mythtv-fixes-glvdpau20405-4.patch.gz