Update errormessage

nsr does not differentiate between SERVFAIL and NXDOMAIN,
so make this more clear.
Implement reverse lookup output (IPv4)

Add reverse lookup for IPv4 addresses in dotted decimal
formatting.
Implement reverse lookup output (IPv6, subset)

Add reverse lookup with "correct" output formatting for IPv6
in hexadecimal colon format. While the most common, this is only
a subset of all correct IPv6 formats.

Regexp::Common in version 20130301 has support for a correct IPv6
regexp, but I did not want to add an external dependency. This is
a dirty debug helper; elevating it from that to general purpose tool
will take a lot more :)