APM: allow for separate calibration of airspeed/barometer

this is useful just before takeoff, to account for temperature changes

ArduPlane/GCS_Mavlink.pde

@@ -1038,9 +1038,13 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
 
             case MAV_CMD_PREFLIGHT_CALIBRATION:
                 if (packet.param1 == 1 ||
-                    packet.param2 == 1 ||
-                    packet.param3 == 1) {
+                    packet.param2 == 1) {
                     startup_IMU_ground(true);
+                } else if (packet.param3 == 1) {
+                    init_barometer();
+                    if (airspeed.enabled()) {
+                        zero_airspeed();
+                    }
                 }
                 if (packet.param4 == 1) {
                     trim_radio();

ArduPlane/sensors.pde

@@ -34,6 +34,7 @@ static void read_airspeed(void)
 static void zero_airspeed(void)
 {
     airspeed.calibrate(mavlink_delay);
+    gcs_send_text_P(SEVERITY_LOW,PSTR("zero airspeed calibrated"));
 }
 
 #endif // HIL_MODE != HIL_MODE_ATTITUDE

ArduPlane/system.pde

@@ -450,7 +450,6 @@ static void startup_IMU_ground(bool force_accel_level)
         // initialize airspeed sensor
         // --------------------------
         zero_airspeed();
-        gcs_send_text_P(SEVERITY_LOW,PSTR("zero airspeed calibrated"));
     } else {
         gcs_send_text_P(SEVERITY_LOW,PSTR("NO airspeed"));
     }