Set explicit SSL_verify_mode in real-servers.t

The newer versions of IO::Socket::SSL (v1.79 and above) have started
warning loudly if SSL_verify_mode is not set explicitly, because the
default will soon change from SSL_VERIFY_NONE to SSL_VERIFY_PEER.
Changed test ports so they can be run in parallel

Changed the test ports so that all tests use different ports.

Updated t/TestServer.pm so that it no longer provides a default port if
one is not provided to new(). Added a comment to explain that this is to
ensure that tests always run correctly in parallel.
Updated comment to reflect reality

t/TestServer.pm no longer uses the port number to determine whether to
act as a proxy, but instead keys off an "act_as_proxy" option.
Updated CHANGES and THANKS
Added TODO about dealing with test ports better