Make the number of output surfaces allocated by vo_vdpau configurable
and allow queuing multiple future frames with the VDPAU frame timing
functionality. There are two known issues that could be polished in
the future for particularly long queue time cases. First, toplevel
code should possibly wait for the queued changes to finish displaying
in some situations like switching files. Second, the VO can block
waiting for a surface to become available, and in the worst case this
wait can be almost as long as the maximum queuing time (potentially
causing audio underruns). However those issues are not high priority.
