Initial minimal working tracerestrict implementation.

This is a port of the tracerestrict/routing restrictions feature
from TTDPatch.
At present this implements if tests (train length only),
and pathfinder deny and penalty actions.
This requires the use of YAPF. Note that restrictions are only evaluated
within the YAPF lookahead distance.

src/rail_map.h

@@ -479,6 +479,18 @@ static inline bool HasOnewaySignalBlockingTrackdir(TileIndex tile, Trackdir td)
 			!HasSignalOnTrackdir(tile, td) && IsOnewaySignal(tile, TrackdirToTrack(td));
 }
 
+static inline bool IsRestrictedSignal(TileIndex t)
+{
+	assert(GetRailTileType(t) == RAIL_TILE_SIGNALS);
+	return (bool) GB(_m[t].m2, 12, 1);
+}
+
+static inline void SetRestrictedSignal(TileIndex t, bool is_restricted)
+{
+	assert(GetRailTileType(t) == RAIL_TILE_SIGNALS);
+	SB(_m[t].m2, 12, 1, is_restricted);
+}
+
 
 RailType GetTileRailType(TileIndex tile);