Re: More protocol.h replacements this time into walsender.c

Committed.  I noticed that there are several characters with no match in
protocol.h.  It might be worth adding those.

In walsender.c:

    1537:    pq_sendbyte(ctx->out, 'w');
    2353:        case 'r':
    2357:        case 'h':
    2361:        case 'p':
    2755:    pq_sendbyte(&output_message, 's');
    3367:    pq_sendbyte(&output_message, 'w');
    4138:    pq_sendbyte(&output_message, 'k');

In walreceiver.c:

    829:        case 'w':                /* WAL records */
    853:        case 'k':                /* Keepalive */
    1133:    pq_sendbyte(&reply_message, 'r');
    1237:    pq_sendbyte(&reply_message, 'h');

In logical/worker.c:

3854:                    if (c == 'w')
3876:                    else if (c == 'k')
3895:                    else if (c == 's')    /* Primary status update */
4127:    pq_sendbyte(reply_message, 'r');
4298:    pq_sendbyte(request_message, 'p');

-- 
nathan