Security: Cross Protocol Scripting protection.

This is an attempt at mitigating problems due to cross protocol
scripting, an attack targeting services using line oriented protocols
like Redis that can accept HTTP requests as valid protocol, by
discarding the invalid parts and accepting the payloads sent, for
example, via a POST request.

For this to be effective, when we detect POST and Host: and terminate
the connection asynchronously, the networking code was modified in order
to never process further input. It was later verified that in a
pipelined request containing a POST command, the successive commands are
not executed.
int clientsCronHandleTimeout(client *c, mstime_t now_ms) {
    time_t now = now_ms/1000;

    if (server.maxidletime &&
        !(c->flags & CLIENT_SLAVE) &&    /* no timeout for slaves */
        !(c->flags & CLIENT_MASTER) &&   /* no timeout for masters */
        !(c->flags & CLIENT_BLOCKED) &&  /* no timeout for BLPOP */
        !(c->flags & CLIENT_PUBSUB) &&   /* no timeout for Pub/Sub clients */
        (now - c->lastinteraction > server.maxidletime))
    {
        serverLog(LL_VERBOSE,"Closing idle client");
        freeClient(c);
        return 1;
    } else if (c->flags & CLIENT_BLOCKED) {
        /* Blocked OPS timeout is handled with milliseconds resolution.
         * However note that the actual resolution is limited by
         * server.hz. */

        if (c->bpop.timeout != 0 && c->bpop.timeout < now_ms) {
            /* Handle blocking operation specific timeout. */
            replyToBlockedClientTimedOut(c);
            unblockClient(c);
        } else if (server.cluster_enabled) {
            /* Cluster: handle unblock & redirect of clients blocked
             * into keys no longer served by this server. */
            if (clusterRedirectBlockedClientIfNeeded(c))
                unblockClient(c);
        }
    }
    return 0;
}

int clientsCronHandleTimeout(client *c, mstime_t now_ms) {
    time_t now = now_ms/1000;

    if (server.maxidletime &&
        !(c->flags & CLIENT_SLAVE) &&    /* no timeout for slaves */
        !(c->flags & CLIENT_MASTER) &&   /* no timeout for masters */
        !(c->flags & CLIENT_BLOCKED) &&  /* no timeout for BLPOP */
        !(c->flags & CLIENT_PUBSUB) &&   /* no timeout for Pub/Sub clients */
        (now - c->lastinteraction > server.maxidletime))
    {
        serverLog(LL_VERBOSE,"Closing idle client");
        freeClient(c);
        return 1;
    } else if (c->flags & CLIENT_BLOCKED) {
        /* Blocked OPS timeout is handled with milliseconds resolution.
         * However note that the actual resolution is limited by
         * server.hz. */

        if (c->bpop.timeout != 0 && c->bpop.timeout < now_ms) {
            /* Handle blocking operation specific timeout. */
            replyToBlockedClientTimedOut(c);
            unblockClient(c);
        } else if (server.cluster_enabled) {
            /* Cluster: handle unblock & redirect of clients blocked
             * into keys no longer served by this server. */
            if (clusterRedirectBlockedClientIfNeeded(c))
                unblockClient(c);
        }
    }
    return 0;
}
