(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.

map.h

@@ -35,6 +35,14 @@ uint ScaleByMapSize(uint); // Scale relative to the number of tiles
 uint ScaleByMapSize1D(uint); // Scale relative to the circumference of the map
 
 typedef uint32 TileIndex;
+
+typedef enum {
+	OWNER_TOWN			= 0xf,	// a town owns the tile
+	OWNER_NONE			= 0x10,	// nobody owns the tile
+	OWNER_WATER			= 0x11,	// "water" owns the tile
+	OWNER_SPECTATOR	= 0xff,	// spectator in MP or in scenario editor
+} Owner;
+
 enum {
 	INVALID_TILE = (uint32) -1
 };