1. The local domain is now ".weave.local", which is safer from TLD
pollution
2. If the name given for an IP isn't a subdomain of the local domain,
ignore it
* In general we'll have an IP address and a subnet mask for the weave
network address; account for this in the zone DB and in the HTTP
server.
* Use the net.IP type rather than string, which gives us a bit more
generality (in theory it'll deal with Ipv6 too) and validation (we
attempt to parse the input)