Change to how playback will retry if prebuffer wait timed out. Will abort after 100 attempts

Backported VDPAU upto upstream svn #20549.

Fixes include:

#20546: Prevent a VDPAU segmentation fault when toggling deinterlacing.

#20547: Ensure toggling VDPAU deinterlacing is thread safe. Closes #6534.

Deinterlacing can be enabled/disabled in different threads which can be an issue for hardware deinterlacers

#20548: Minor VDPAU initialisation improvements.

#20549: Minor VDPAU tidy up.

Patch is available at:

http://www.avenard.org/files/media/vdpau/mythtv-fixes-glvdpau20549.patch.gz