max_cpus preference ignored.

[Didactylos]

When max_cpus was replaced with max_ncpus_pct, the old setting was removed from the parser. This is an error; the old setting still exists in many preference sets, and is still set by some projects.

This will have the effect that BOINC 6 will run on all cores/cpus after upgrading. Because this is such a critical setting, I have made this ticket a blocker.

max_cpus should still be used any time when max_ncpus_pct is not present.