Plane: add reverse_thrust option when in landing pattern

ArduPlane/defines.h

@@ -144,6 +144,7 @@ enum {
     USE_REVERSE_THRUST_CRUISE                   = (1<<8),
     USE_REVERSE_THRUST_FBWB                     = (1<<9),
     USE_REVERSE_THRUST_GUIDED                   = (1<<10),
+    USE_REVERSE_THRUST_AUTO_LANDING_PATTERN     = (1<<11),
 };
 
 enum FlightOptions {

ArduPlane/reverse_thrust.cpp

@@ -61,6 +61,10 @@ bool Plane::allow_reverse_thrust(void) const
         allow |= (g.use_reverse_thrust & USE_REVERSE_THRUST_AUTO_WAYPOINT) &&
                     (nav_cmd == MAV_CMD_NAV_WAYPOINT ||
                      nav_cmd == MAV_CMD_NAV_SPLINE_WAYPOINT);
+
+        // we are on a landing pattern
+        allow |= (g.use_reverse_thrust & USE_REVERSE_THRUST_AUTO_LANDING_PATTERN) &&
+                mission.get_in_landing_sequence_flag();
         }
         break;