Fixed nearby bugs (in linux_alarm()):
- the itimer for the alarm was relative to the epoch instead of relative
to the boot time. This was harmless because the itimer's interval is 0.
- the seconds arg was not checked for validity before converting it to a
possibly different value.
- printf format errors.
Improvements:
Don't use splclock(). splsoftclock() suffices. Don't complicate things
by micro-optimizing interrupt latency.
Minor improvements:
Various micro-optimizations to exploit the specialness of the alarm itimer
and the value 0.
882fdeae66