(svn r1834) - Fix: NPF does not check the owner of its target, busses try to enter other players' depots. TODO

- Add: asserts to find the v->u.rail.track == 0 problem.
- Add: IsValidDepot(), IsValidTown(), IsValidSign(), IsValidVehicle(), IsValidStation()
- Add: GetTileOwner(), IsTileOwner()
- Codechange: Replaced IsShipDepotTile(), IsTrainDepotTile(), IsRoadDepotTile() by IsTileDepotType().
- Codechange: typedeffed the MAP_OWNERS as Owner. Should be used as variable type.
- Codechange: Replaced a few uint by TileIndex.

tile.h

@@ -57,4 +57,14 @@ static inline bool IsTileType(TileIndex tile, TileType type)
 	return GetTileType(tile) == type;
 }
 
+static inline bool GetTileOwner(TileIndex tile)
+{
+	return _map_owner[tile];
+}
+
+static inline bool IsTileOwner(TileIndex tile, Owner owner)
+{
+	return GetTileOwner(tile) == owner;
+}
+
 #endif