(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.

ttd.h

@@ -510,13 +510,6 @@ enum SpecialStrings {
 
 typedef void PlaceProc(uint tile);
 
-enum MAP_OWNERS {
-	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
-};
-
 VARDEF bool _savegame_sort_dirty;
 VARDEF byte _savegame_sort_order;