APM_Control: scale controllers for altitude

this allows the attitude controllers to better handle a wider range of
altitudes

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>

libraries/APM_Control/AP_PitchController.cpp

@@ -143,7 +143,7 @@ int32_t AP_PitchController::_get_rate_out(float desired_rate, float scaler, bool
 
 	// Calculate equivalent gains so that values for K_P and K_I can be taken across from the old PID law
     // No conversion is required for K_D
-	float kp_ff = max((_K_P - _K_I * _tau) * _tau  - _K_D , 0);
+	float kp_ff = max((_K_P - _K_I * _tau) * _tau  - _K_D , 0) / _ahrs->get_EAS2TAS();
 	
 	// Calculate the demanded control surface deflection
 	// Note the scaler is applied again. We want a 1/speed scaler applied to the feed-forward

libraries/APM_Control/AP_RollController.cpp

@@ -82,15 +82,16 @@ int32_t AP_RollController::_get_rate_out(float desired_rate, float scaler, bool
 	}
 	_last_t = tnow;
 	
-	// Calculate equivalent gains so that values for K_P and K_I can be taken across from the old PID law
-    // No conversion is required for K_D
-	float kp_ff = max((_K_P - _K_I * _tau) * _tau  - _K_D , 0);
-	float ki_rate = _K_I * _tau;
 
 	if (_ahrs == NULL) {
         // can't control without a reference
         return 0;
     }
+
+	// Calculate equivalent gains so that values for K_P and K_I can be taken across from the old PID law
+    // No conversion is required for K_D
+	float ki_rate = _K_I * _tau;
+	float kp_ff = max((_K_P - _K_I * _tau) * _tau  - _K_D , 0)/_ahrs->get_EAS2TAS();
 	float delta_time    = (float)dt * 0.001f;
 	
 	// Limit the demanded roll rate