Copter: load accel throttle I term from attitude controller input

Previously we loaded up the I term from the pilot's input but a more reliable method is to get what was passed into the attitude controller.  In particular the addition of the acro-thr-mid parameter means the pilot's input must be interpreted differently for different flight modes.

ArduCopter/Attitude.cpp

@@ -243,8 +243,10 @@ float Copter::get_surface_tracking_climb_rate(int16_t target_rate, float current
 }
 
 // set_accel_throttle_I_from_pilot_throttle - smoothes transition from pilot controlled throttle to autopilot throttle
-void Copter::set_accel_throttle_I_from_pilot_throttle(float pilot_throttle)
+void Copter::set_accel_throttle_I_from_pilot_throttle()
 {
+    // get last throttle input sent to attitude controller
+    float pilot_throttle = constrain_float(attitude_control.get_throttle_in(), 0.0f, 1.0f);
     // shift difference between pilot's throttle and hover throttle into accelerometer I
     g.pid_accel_z.set_integrator((pilot_throttle-motors.get_throttle_hover()) * 1000.0f);
 }

ArduCopter/Copter.h

@@ -691,7 +691,7 @@ private:
     float get_surface_tracking_climb_rate(int16_t target_rate, float current_alt_target, float dt);
     void auto_takeoff_set_start_alt(void);
     void auto_takeoff_attitude_run(float target_yaw_rate);
-    void set_accel_throttle_I_from_pilot_throttle(float pilot_throttle);
+    void set_accel_throttle_I_from_pilot_throttle();
     void update_poscon_alt_max();
     void rotate_body_frame_to_NE(float &x, float &y);
     void gcs_send_heartbeat(void);

ArduCopter/flight_mode.cpp

@@ -274,7 +274,7 @@ void Copter::exit_mode(control_mode_t old_control_mode, control_mode_t new_contr
     // smooth throttle transition when switching from manual to automatic flight modes
     if (mode_has_manual_throttle(old_control_mode) && !mode_has_manual_throttle(new_control_mode) && motors.armed() && !ap.land_complete) {
         // this assumes all manual flight modes use get_pilot_desired_throttle to translate pilot input to output throttle
-        set_accel_throttle_I_from_pilot_throttle(get_pilot_desired_throttle(channel_throttle->get_control_in()));
+        set_accel_throttle_I_from_pilot_throttle();
     }
 
     // cancel any takeoffs in progress