Correct keep-alive responses to HTTP 1.0 clients.

Since the proxy requests comes from NodeJS's HTTP 1.1 request client, a
backend server may default to setting Connection: keep-alive in its
response. However, the real HTTP 1.0 client may not be able to
handle that.

Force HTTP 1.0 client's to Connection: close, unless the client
explicitly supports keep-alive.
Don't test raw HTTP 1.0 requests over HTTPS.
Merge pull request #407 from GUI/master

Correct keep-alive responses to HTTP 1.0 clients