(svn r23254) [1.1] -Backport from trunk:

- Fix: [NewGRF] Run StartupEngines() if NewGRFs changed during loading a savegame, just like it's running when NewGRFs are changed during a game (r23083)
- Fix: Account for snow line table when determining the snow line for building houses (r23082)
- Fix: [NewGRF] If a NewGRF overrides a default house the minimum start year for that house was set to 1930 [FS#4794] (r23059)
- Fix: [NoAI] AIOrder::GetOrderCount() did not hide implicit orders (r23057)

src/ai/api/ai_order.cpp

@@ -190,7 +190,7 @@ static const Order *ResolveOrder(VehicleID vehicle_id, AIOrder::OrderPosition or
 
 /* static */ int32 AIOrder::GetOrderCount(VehicleID vehicle_id)
 {
-	return AIVehicle::IsValidVehicle(vehicle_id) ? ::Vehicle::Get(vehicle_id)->GetNumOrders() : -1;
+	return AIVehicle::IsValidVehicle(vehicle_id) ? ::Vehicle::Get(vehicle_id)->GetNumManualOrders() : -1;
 }
 
 /* static */ TileIndex AIOrder::GetOrderDestination(VehicleID vehicle_id, OrderPosition order_position)

src/engine.cpp

@@ -650,6 +650,10 @@ void StartupOneEngine(Engine *e, Date aging_date)
 	}
 }
 
+/**
+ * Start/initialise all our engines. Must be called whenever there are changes
+ * to the NewGRF config.
+ */
 void StartupEngines()
 {
 	Engine *e;

src/newgrf.cpp

@@ -1679,13 +1679,6 @@ static ChangeInfoResult TownHouseChangeInfo(uint hid, int numinfo, int prop, Byt
 					housespec->cargo_acceptance[2] = 0;
 				}
 
-				/**
-				 * New houses do not (currently) expect to have a default start
-				 * date before 1930, as this breaks the build date stuff.
-				 * @see FinaliseHouseArray() for more details.
-				 */
-				if (housespec->min_year < 1930) housespec->min_year = 1930;
-
 				_loaded_newgrf_features.has_newhouses = true;
 				break;
 			}

src/saveload/afterload.cpp

@@ -2595,6 +2595,11 @@ bool AfterLoadGame()
 		}
 	}
 
+	/* When any NewGRF has been changed the availability of some vehicles might
+	 * have been changed too. e->company_avail must be set to 0 in that case
+	 * which is done by StartupEngines(). */
+	if (gcf_res != GLC_ALL_GOOD) StartupEngines();
+
 	/* Road stops is 'only' updating some caches */
 	AfterLoadRoadStops();
 	AfterLoadLabelMaps();

src/town_cmd.cpp

@@ -2095,7 +2095,7 @@ static bool BuildTownHouse(Town *t, TileIndex tile)
 
 	/* Above snow? */
 	int land = _settings_game.game_creation.landscape;
-	if (land == LT_ARCTIC && z >= _settings_game.game_creation.snow_line) land = -1;
+	if (land == LT_ARCTIC && z >= HighestSnowLine()) land = -1;
 
 	uint bitmask = (1 << rad) + (1 << (land + 12));