MEDIUM: http: restrict the HTTP version token to 1 digit as per RFC7230

MEDIUM: http: restrict the HTTP version token to 1 digit as per RFC7230

While RFC2616 used to allow an undeterminate amount of digits for the
major and minor components of the HTTP version, RFC7230 has reduced
that to a single digit for each.

If a server can't properly parse the version string and falls back to 0.9,
it could then send a head-less response whose payload would be taken for
headers, which could confuse downstream agents.

Since there's no more reason for supporting a version scheme that was
never used, let's upgrade to the updated version of the standard. It is
still possible to enforce support for the old behaviour using options
accept-invalid-http-request and accept-invalid-http-response.

It would be wise to backport this to 1.5 as well just in case.