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.
set MX=YES in your .config file if the DOMAIN specified in
the .config file is actually an mx record.
currently only supported when using nslookup and not drill.
added SILENT mode:
if SILENT is set to NO the output and the logmessages
remain the same.
if SILENT is set to something else than NO or not set then
neither will there be an output nor a log message as long
as the ip-address doesn't change
