AC_AttitudeControl: fixed external tail gyro with no flybar

this sets up the tail pass-through for acro mode

libraries/AC_AttitudeControl/AC_AttitudeControl.h

@@ -136,7 +136,7 @@ public:
     void rate_ef_roll_pitch_yaw(float roll_rate_ef, float pitch_rate_ef, float yaw_rate_ef);
 
     // rate_bf_roll_pitch_yaw - attempts to maintain a roll, pitch and yaw rate (all body frame)
-    void rate_bf_roll_pitch_yaw(float roll_rate_bf, float pitch_rate_bf, float yaw_rate_bf);
+    virtual void rate_bf_roll_pitch_yaw(float roll_rate_bf, float pitch_rate_bf, float yaw_rate_bf);
 
     //
     // rate_controller_run - run lowest level body-frame rate controller and send outputs to the motors

libraries/AC_AttitudeControl/AC_AttitudeControl_Heli.cpp

@@ -86,6 +86,14 @@ void AC_AttitudeControl_Heli::passthrough_bf_roll_pitch_rate_yaw(float roll_pass
     _rate_bf_target.z += _rate_bf_desired.z;
 }
 
+// subclass non-passthrough too, for external gyro, no flybar
+void AC_AttitudeControl_Heli::rate_bf_roll_pitch_yaw(float roll_rate_bf, float pitch_rate_bf, float yaw_rate_bf)
+{
+    _passthrough_yaw = yaw_rate_bf;
+
+    AC_AttitudeControl::rate_bf_roll_pitch_yaw(roll_rate_bf, pitch_rate_bf, yaw_rate_bf);
+}
+
 //
 // rate controller (body-frame) methods
 //

libraries/AC_AttitudeControl/AC_AttitudeControl_Heli.h

@@ -49,6 +49,9 @@ public:
     // passthrough_bf_roll_pitch_rate_yaw - roll and pitch are passed through directly, body-frame rate target for yaw
     void passthrough_bf_roll_pitch_rate_yaw(float roll_passthrough, float pitch_passthrough, float yaw_rate_bf);
 
+	// subclass non-passthrough too, for external gyro, no flybar
+	void rate_bf_roll_pitch_yaw(float roll_rate_bf, float pitch_rate_bf, float yaw_rate_bf) override;
+
 	// rate_controller_run - run lowest level body-frame rate controller and send outputs to the motors
 	// should be called at 100hz or more
 	virtual void rate_controller_run();