Change behaviour of connection or server response when the request is
version 1.0 and the Connection: keep-alive header is not present.
1. If the response is also version 1.0, then connection is closed if the
server keep-alive header is not present.
2. If the response is version 1.1, then the keep-alive header is added
when downgrading to version 1.0.
Closes#1614