added support for mx records and some sort of silent ouput/logs

MX Records:
        if the DOMAIN specified in the .config file is actually an mx
        record then set MX=YES in your .config file.
	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.