Changed the way the existence of config files is checked. It may be a
bit slower than before when there are many config files but maybe it
avoids other trouble.
Updated the sample config.
- Changed default IP check site to ifconfig.me
- Added a switch to use _drill_ instead of _nslookup_ because FreeBSD
10 switched from _bind_ to _unbound_
- Renamed _$HOSTNAME_ to _$DOMAIN_ to work around potential conflicts
with _$HOSTNAME_ that's set by the host itself
chris