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If the VDPAU_DRIVER environment variable is not set, use DRI2Connect to query
the VDPAU driver name from the X server.
Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>

* Add a --with-module-dir configure parameter.

* Pass the moduledir into the wrapper.  Use it to construct the path to search
  for drivers.  Require drivers to end in a ".1" version, in case we ever want
  to rev. the interface between the wrapper and the drivers.

* If no driver is found in the new module dir, look for one in the default
  search paths.  This is intended to find libvdpau_nvidia.so for drivers that
  predate the change to move it, and can be removed in the future.

* Stash the moduledir into vdpau.pc.  Drivers can find this with
  `pkg-config --variable=moduledir vdpau`.

* Add a version to libvdpau_trace.so in case the interface between it and
  libvdpau.so ever changes.

* Install libvdpau_trace.so.1 to moduledir instead of libdir.
Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>

Without printouts, it's impossible to tell why VDPAU initialization fails when
it can't open the backend or trace libraries or can't find various symbols.