If a SOCKS5 client insists on authentication, allow it to
negotiate a connection with Tor's SOCKS server successfully.
Any credentials the client provides are ignored.
This allows Tor to work with SOCKS5 clients that can only
support 'authenticated' connections.
Also add a bunch of basic unit tests for SOCKS4/4a/5 support
in buffers.c.
This is needed for IOCP, since telling the IOCP backend about all
your CPUs is a good idea. It'll also come in handy with asn's
multithreaded crypto stuff, and for people who run servers without
reading the manual.
