This provides a more traditional set of library function calls than the
VDPAU specification defines. Furthermore, this has libvdpau.so as a
conditional run-time linking dependency.

Note that this requires libvdpau 0.6 or later (0.4.1-8 on Debian) at
run-time due to a bug in libvdpau versions 0.4 through 0.5.