[dns-operations] open resolver testing tool

[Duane Wessels]

If anyone has the need to test particular addresses for the
presence of open resolvers, please feel free to use this tool:

http://dns.measurement-factory.com/cgi-bin/openresolvercheck.pl

It will send a single "recursion desired" query to a target address.
If that query is forwarded to our authoritative server, the host
has an open resolver running at that address.

Duane W.