- Minor features:
    - Try to use system facilities for enumerating local interface
      addresses, before falling back to our old approach (which was
      binding a UDP socket, and calling getsockname() on it). That
      approach was confusing people whose draconian firewall software
      didn't like binding to UDP sockets, regardless of whether
      packets were sent. Now we try to use getifaddrs(), SIOCGIFCONF,
      or GetAdaptersAddresses(), depending on what the system
      supports. Resolves ticket #1827.