Change the fifo size from being statically tuned for a Mac Pro with 4 CPUs to dynamic...

Change the fifo size from being statically tuned for a Mac Pro with 4 CPUs to dynamically adjust according to how many processors are available. 8 extra buffers in the fifo per CPU available. Hopefully this will make the single CPU systems run at pretty much the same speed as before (although they may still be slower if they are low on memory and start thrashing the pager).

git-svn-id: svn://localhost/HandBrake/trunk@1023 b64f7644-9d1e-0410-96f1-a4d463321fa5