Because recalculate is only called once or twice for long sleeps,

Because recalculate is only called once or twice for long sleeps,
not every second forever while the process is sleeping, we have
to manually call it to resynchronize p_cpbase on wakeup or it
will wrap if the process was sleeping long enough (e.g. ~10 min
with the ACPI timer) and really mess up the nticks calculation.

The bug could very rarely result in an integer divide by 0 crash.

Reported-by: David Rhodus