Finished adding a '-w' option.

src/modules/mavlink/mavlink_receiver.cpp

@@ -181,6 +181,10 @@ MavlinkReceiver::handle_message(mavlink_message_t *msg)
 			break;
 		}
 	}
+
+    /* If we've received a valid message, mark the flag indicating so.
+       This is used in the '-w' command-line flag. */
+    _mavlink->set_has_received_messages(true);
 }
 
 void