Copter: add support for DO_PARACHUTE from GCS

Mission command support was already included but this adds support for
DO_PARACHUTE received as a COMMAND_LONG message which are sent from the
GCS when the command should be executed immediately

ArduCopter/GCS_Mavlink.pde

@@ -1218,6 +1218,29 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
 #endif
             break;
 
+#if PARACHUTE == ENABLED
+        case MAV_CMD_DO_PARACHUTE:
+            // configure or release parachute
+            result = MAV_RESULT_ACCEPTED;
+            switch ((uint16_t)packet.param1) {
+                case PARACHUTE_DISABLE:
+                    parachute.enabled(false);
+                    Log_Write_Event(DATA_PARACHUTE_DISABLED);
+                    break;
+                case PARACHUTE_ENABLE:
+                    parachute.enabled(true);
+                    Log_Write_Event(DATA_PARACHUTE_ENABLED);
+                    break;
+                case PARACHUTE_RELEASE:
+                    // treat as a manual release which performs some additional check of altitude
+                    parachute_manual_release();
+                    break;
+                default:
+                    result = MAV_RESULT_FAILED;
+                    break;
+            }
+#endif
+
         case MAV_CMD_DO_MOTOR_TEST:
             // param1 : motor sequence number (a number from 1 to max number of motors on the vehicle)
             // param2 : throttle type (0=throttle percentage, 1=PWM, 2=pilot throttle channel pass-through. See MOTOR_TEST_THROTTLE_TYPE enum)