Modify http.lua to do a host lookup first, to determine the right address family to use (previously tcp was the default).

The attached patch might be nonsense or just as well not the right way™ to handle the problem.
I'm submitting this for discussion.

With this patch applied I can use the examples from #83 without problems: The ipv6 requests succeed just fine. Plus, as a bonus, ipv4 requests still work... :)