Reorganized io::net::ip, creating separate Ipv[46]Addr types and adding version-specific methods

This adds several address inspection methods, such as `is_loopback`, `is_multicast`, and
`is_private`, as well as improving formatting (It adds support for `::`-shortening addresses and
fixes :: and ::1) and adding methods to convert between different IP versions.

The variants `IpAddr::Ipv4Addr` and `Ipv6Addr` were limiting: There are `is_...` methods that
make sense for either v4 or v6 addresses but not for both versions, and there's no way to define
methods for only one variant of an enum, so the variants are promoted to independent types.

The IpAddr enum now wraps the Ipv4Addr and Ipv6Addr types:

  enum IpAddr { V4(Ipv4Addr), V6(Ipv6Addr) }

Addresses are created as:

  Ipv4Addr::new(1, 2, 3, 4) -> Ipv4Addr
  IpAddr::new_v4(1, 2, 3, 4) -> IpvAddr::V4(Ipv4Addr)

or using FromStr for any of the three address types.

IP addresses can be passed as their core types (IPvXAddr), as IpAddr, or using the trait
ToIpAddr, which is implemented for Ipv4Addr, Ipv6Addr and IpAddr.

Author: ktossell

src/libstd/old_io/net/addrinfo.rs

@@ -120,7 +120,7 @@ mod test {
     fn dns_smoke_test() {
         let ipaddrs = get_host_addresses("localhost").unwrap();
         let mut found_local = false;
-        let local_addr = &Ipv4Addr(127, 0, 0, 1);
+        let local_addr = &IpAddr::new_v4(127, 0, 0, 1);
         for addr in ipaddrs.iter() {
             found_local = found_local || addr == local_addr;
         }