(svn r16909) -Fix [FS#2996]: NewGRF stations would be triggering assertions all over the place when using the more advanced station types.

-Change: make (rail) waypoints sub classes of 'base stations', make buoys waypoints and unify code between them where possible.

src/ai/api/ai_waypoint.cpp

@@ -22,7 +22,7 @@
 {
 	if (!AIRail::IsRailWaypointTile(tile)) return WAYPOINT_INVALID;
 
-	return ::GetWaypointIndex(tile);
+	return ::GetStationIndex(tile);
 }
 
 /* static */ char *AIWaypoint::GetName(WaypointID waypoint_id)