[MINOR] print usage on the stats sockets upon invalid commands

When issuing commands on the unix socket, there's no way to
know if the result is empty or if the command is wrong. This
patch makes invalid command return a help message.

src/proto_uxst.c

@@ -78,6 +78,18 @@ static struct protocol proto_unix = {
 	.nb_listeners = 0,
 };
 
+const char unix_sock_usage_msg[] =
+        "Unknown command. Please enter one of the following commands only :\n"
+        "  show info   : report information about the running process\n"
+        "  show stat   : report counters for each proxy and server\n"
+        "  show errors : report last request and response errors for each proxy\n"
+        "  show sess   : report the list of current sessions\n"
+	"\n";
+
+const struct chunk unix_sock_usage = {
+        .str = (char *)&unix_sock_usage_msg,
+        .len = sizeof(unix_sock_usage_msg)-1
+};
 
 /********************************
  * 1) low-level socket functions
@@ -666,7 +678,7 @@ int uxst_req_analyser_stats(struct session *s, struct buffer *req, int an_bit)
 			*p = '\0';
 			if (!unix_sock_parse_request(s, line)) {
 				/* invalid request */
-				buffer_shutw_now(s->rep);
+				stream_int_retnclose(s->req->prod, &unix_sock_usage);
 				s->ana_state = 0;
 				req->analysers = 0;
 				return 0;