Plane: handle TERRAIN_CHECK requests

ArduPlane/GCS_Mavlink.pde

@@ -1473,8 +1473,9 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
 #endif
 
     case MAVLINK_MSG_ID_TERRAIN_DATA:
+    case MAVLINK_MSG_ID_TERRAIN_CHECK:
 #if HAVE_AP_TERRAIN
-        terrain.handle_data(msg);
+        terrain.handle_data(chan, msg);
 #endif
         break;
         

ArduPlane/Parameters.pde

@@ -867,9 +867,11 @@ const AP_Param::Info var_info[] PROGMEM = {
     // @Path: ../libraries/AP_RangeFinder/RangeFinder.cpp
     GOBJECT(sonar,                  "RNGFND", RangeFinder),
 
+#if HAVE_AP_TERRAIN
     // @Group: TERRAIN
     // @Path: ../libraries/AP_Terrain/AP_Terrain.cpp
     GOBJECT(terrain,                "TERRAIN_", AP_Terrain),
+#endif
 
     // RC channel
     //-----------