command: add COMMAND_RETURN_IDLE

Eliminate the hack in handle_idle().

src/OtherCommands.cxx

@@ -310,6 +310,5 @@ handle_idle(struct client *client,
 	/* enable "idle" mode on this client */
 	client_idle_wait(client, flags);
 
-	/* return value is "1" so the caller won't print "OK" */
-	return (enum command_return)1;
+	return COMMAND_RETURN_IDLE;
 }

src/client_event.c

@@ -77,6 +77,7 @@ client_in_event(G_GNUC_UNUSED GIOChannel *source, GIOCondition condition,
 	ret = client_read(client);
 	switch (ret) {
 	case COMMAND_RETURN_OK:
+	case COMMAND_RETURN_IDLE:
 	case COMMAND_RETURN_ERROR:
 		break;
 

src/command.h

@@ -31,6 +31,12 @@ enum command_return {
 	 */
 	COMMAND_RETURN_OK,
 
+	/**
+	 * The connection is now in "idle" mode, and no response shall
+	 * be generated.
+	 */
+	COMMAND_RETURN_IDLE,
+
 	/**
 	 * There was an error.  The "ACK" response was sent to the
 	 * client.