[PATCH] Correct the version sent in protocol negotiation

Our protocol doc describes protocol negotiation message will send latest
minor version. However that field is a 4-byte one. The actual
implementation sends full version including the major part:

static void
SendNegotiateProtocolVersion(List *unrecognized_protocol_options)
{
    StringInfoData buf;
    ListCell   *lc;

    pq_beginmessage(&buf, PqMsg_NegotiateProtocolVersion);
    pq_sendint32(&buf, FrontendProtocol);
    pq_sendint32(&buf, list_length(unrecognized_protocol_options));
    foreach(lc, unrecognized_protocol_options)
        pq_sendstring(&buf, lfirst(lc));
    pq_endmessage(&buf);

    /* no need to flush, some other message will follow */
}

The patch included just clarifies this behavior by removing "minor" from
"newest minor version".