ICustomTerrain; more bridge code

OpenRa.Game/World.cs

@@ -4,6 +4,7 @@ using OpenRa.Effects;
 using OpenRa.Support;
 using OpenRa.FileFormats;
 using OpenRa.Graphics;
+using OpenRa.Traits;
 
 namespace OpenRa
 {
@@ -21,6 +22,9 @@ namespace OpenRa
 		public readonly Map Map;
 		public readonly TileSet TileSet;
 
+		// for tricky things like bridges.
+		public readonly ICustomTerrain[,] customTerrain = new ICustomTerrain[128, 128];
+
 		public readonly WorldRenderer WorldRenderer;
 		internal readonly Minimap Minimap;