Copter: use force_descend option on auto landings

ArduCopter/control_auto.pde

@@ -324,7 +324,7 @@ static void auto_land_run()
     wp_nav.update_loiter();
 
     // call z-axis position controller
-    pos_control.set_alt_target_from_climb_rate(get_throttle_land(), G_Dt);
+    pos_control.set_alt_target_from_climb_rate(get_throttle_land(), G_Dt, true);
     pos_control.update_z_controller();
 
     // roll & pitch from waypoint controller, yaw rate from pilot

ArduCopter/control_land.pde

@@ -112,7 +112,7 @@ static void land_gps_run()
     }
 
     // update altitude target and call position controller
-    pos_control.set_alt_target_from_climb_rate(cmb_rate, G_Dt);
+    pos_control.set_alt_target_from_climb_rate(cmb_rate, G_Dt, true);
     pos_control.update_z_controller();
 }
 
@@ -170,7 +170,7 @@ static void land_nogps_run()
     }
 
     // call position controller
-    pos_control.set_alt_target_from_climb_rate(cmb_rate, G_Dt);
+    pos_control.set_alt_target_from_climb_rate(cmb_rate, G_Dt, true);
     pos_control.update_z_controller();
 }
 

ArduCopter/control_rtl.pde

@@ -377,7 +377,7 @@ static void rtl_land_run()
 
     // call z-axis position controller
     float cmb_rate = get_throttle_land();
-    pos_control.set_alt_target_from_climb_rate(cmb_rate, G_Dt);
+    pos_control.set_alt_target_from_climb_rate(cmb_rate, G_Dt, true);
     pos_control.update_z_controller();
 
     // roll & pitch from waypoint controller, yaw rate from pilot