Handle non-127.0.0.1 IPv4 loopback addresses

In #17901 (moved), we identified some FreeBSD jails and OpenVZ VMs as having no 127.0.0.1. #17901 (moved) deals with those systems that have no loopback at all.

But some FreeBSD jails block access to 127.0.0.1, and have loopback on a valid yet unexpected address, like 127.0.0.2.

Tor could bind to any address in 127/8 (or ::1, see #11360 (moved)) and be accessible locally.

One possible implementation is:

• find all addresses on all loopback interfaces (#17949 (moved))
  • as a fallback, resolve localhost (#17953 (moved)), and check that it's 127.0.0.0/8 or ::1
• choose the address that's closest to 127.0.0.1
• use that address as the bind address
• If there is no 127.0.0.0/8 (or ::1) on the server, reject the *Port with a warning that tells the user to use AF_UNIX (if their system supports it), or supply an explicit IP address if they really want their *Port listening on a non-local address.

Operators can always specify an explicit bind address in the *Port line, so this isn't a serious usability issue.