(svn r2473) - Add: VehicleMayEnterTile(), which checks if the tile owner of a tile is correct for a vehicle to enter it. Based upon glx's code.

- Fix: [ 1203769 ] [NPF] NPF tries to plan over bridges, through tunnels, over level crossings of other players. (glx)
- Codechange: Renamed TRANSPORT_MAX to TRANSPORT_END and added INVALID_TRANSPORT.
- Codechange: Moved IsLevelCrossing() from tile.h to rail.h
- Add: GetCrossingTransportType(), which returns the transport type (road, rail) of both tracks on a level crossing.
- Removed old TODO that was fulfilled already.

openttd.h

@@ -106,7 +106,8 @@ typedef enum TransportTypes {
   TRANSPORT_RAIL = 0,
 	TRANSPORT_ROAD = 1,
 	TRANSPORT_WATER,	// = 2
-	TRANSPORT_MAX			// = 3
+	TRANSPORT_END,
+	INVALID_TRANSPORT = 0xff,
 } TransportType;
 
 typedef struct TileInfo {