Split the cron file so that the hourly, daily, weekly, and monthly
zfs automatic snapshots still happen even if the system is offline
temporarily during the scheduled event, such as during a reboot.
On Debian systems, if anacron is installed, then it is used to run
the /etc/cron.{hourly,daily,weekly,monthly} directories, but not
the /etc/cron.d directory. This means that /etc/cron.d jobs are not
run if the system is offline when crond would usually invoke them.
