(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.

ai_new.c

@@ -1213,7 +1213,7 @@ static void AiNew_CheckVehicle(Player *p, Vehicle *v) {
 
 			// We are already sending him back
 			if (AiNew_GetSpecialVehicleFlag(p, v) & AI_VEHICLEFLAG_SELL) {
-				if (v->type == VEH_Road && IsRoadDepotTile(v->tile) &&
+				if (v->type == VEH_Road && IsTileDepotType(v->tile, TRANSPORT_ROAD) &&
 					(v->vehstatus&VS_STOPPED)) {
 					// We are at the depot, sell the vehicle
 					DoCommandByTile(0, v->index, 0, DC_EXEC, CMD_SELL_ROAD_VEH);