svn commit: r253002 - head

[Simon J. Gerraty]

>We've run as high as -j48 ... number of logical cpu's "times-two" (it was o=
>n a box with 24 logical CPUs).

We've (ok dhw@ has) done a lot of empirical measurement
to determine optimal jobs_factor numbers for various machines.
Right now we are using .75 for boxes with > 16 cores.
For smaller boxes we use up to 1.5

Scaling on NUMA boxes is a sore point ;-)
If someone could get FreeBSD to scale on larger (64 core) NUMA boxes
that would be excellent.