(svn r3946) Add short hand names for common track combinations

rail.h

@@ -500,9 +500,7 @@ static inline bool TracksOverlap(TrackBits bits)
   /* We know that there are at least two tracks present. When there are more
    * than 2 tracks, they will surely overlap. When there are two, they will
    * always overlap unless they are lower & upper or right & left. */
-	return
-		bits != (TRACK_BIT_UPPER | TRACK_BIT_LOWER) &&
-		bits != (TRACK_BIT_LEFT  | TRACK_BIT_RIGHT);
+	return bits != TRACK_BIT_HORZ && bits != TRACK_BIT_VERT;
 }
 
 void DrawTrainDepotSprite(int x, int y, int image, RailType railtype);