requests, default to the previous 60-seconds scheduling method
unless there is any @every_second entries to conserve CPU cycles and
power.
This change also improves scheduling in the default mode by running
as close to the beginning of the minnute as possible by replacing
sleep(3) with nanosleep(2). Previously, the tasks would run anywhere
within the first second of the minute and that offset drifted back
and forth each time cron(8) was engaged.
MFC after: 1 month
7a5c30c5b6