Support CIDR

[pimlott]

jdresolve's recursive resolution is really clever, I love it! I'm not a DNS expert, but I wonder if it could be extended to CIDR (and if this would have any practical benefit). It looks like CIDR reverse DNS methods do not allow for simple discovery of the subnet delegations. You would have to guess at them, and you might have to try several naming conventions (http://faq.he.net/index.php/Reverse_DNS). So it would be inefficient, but it's doable. Does it make sense? I defer to you on that question!