Read `/etc/hosts.autoupdate` which contains DNS hostnames and put an IP NAME
enty into `/etc/hosts`.

The main purpose is to do name-based access control for hosts with a dynamic
DNS entry. Such systems usually don't have a valid PTR record so that name-based
access control with double lookups is not possible.

`hosts-updater` solves this problem by keeping the IP NAME records in the local
hosts(5) database so that also reverse lookups for the IP will yield the intended
name and not the real PTR record (e.g. of a dialup system).

`hosts-updater` is run every 5 minutes from `/etc/cron.d/hosts-updater`.