Send FS state to gcs for AP

ArduPlane/GCS_Mavlink.pde

@@ -28,6 +28,10 @@ static NOINLINE void send_heartbeat(mavlink_channel_t chan)
     uint8_t system_status = MAV_STATE_ACTIVE;
     uint32_t custom_mode = control_mode;
     
+    if (failsafe != FAILSAFE_NONE) {
+        system_status = MAV_STATE_CRITICAL;
+    }
+
     // work out the base_mode. This value is not very useful
     // for APM, but we calculate it as best we can so a generic
     // MAVLink enabled ground station can work out something about