this appears to be a splice from libx264.67.so which was not introduced to 
mainline x264 development.

with some amount of manual downloading and assembly i was able to encode 600 frames 
of big buck bunny per the original demo script at 151 fps on a 3.3 ghz stock i980x 
core i7 on linux 3.1pre with radeon 6970 @ 910mhz/300Ram-Mhz + AMD APP 2.5.  (typically only 1x encoding by multicore cpu alone.)

credit given to original project authors http://li5.ziti.uni-heidelberg.de/x264gpu

James Northrup