Occasional stack overflows

[barrucadu]

Sometimes there's a stack overflow. That's pretty bad.

I think setting a recursion limit in the resolvers will fix it, but that's more intended to deal with malicious upstream nameservers which bounce clients around in a loop. There may also be a bug in the resolver which makes it enter that infinite recursion when it shouldn't.

[barrucadu]

#70 introduces a recursion limit, which will hopefully stop these from happening; but it's still not an ideal solution.