Check all DNS servers for a domain
An error is generated if any server is not functioning, or not authoritative
A warning is generated if any server lags the others in serial-number
v1.7 uploaded 21 Nov 2012 - added support for IPv6 AAAA records
v1.8 updated 26 April 2013 - Allow plugin to work with embedded perl interpreter
v1.9 updated 17 Oct 2013 - Allow plugin to work with embedded perl interpreter ePN
