Default to /proc/cpuinfo for maxTaskPar.prediff core counting.

Instead of explicitly calling out the configurations for which we use
/proc/cpuinfo to determine the core count, default to /proc/cpuinfo and
arrange for failure (by putting a '0' in the .good) when it's not there.

I've tested in enough configurations to cover all the logic paths.

Brad gets credit for this idea and, as a reward, I'll ask him to review it!