move Building et al into Mods/

OpenRA.Game/Traits/World/ResourceLayer.cs

@@ -71,7 +71,7 @@ namespace OpenRA.Traits
 				for (int y = map.YOffset; y < map.YOffset + map.Height; y++)
 				{
 					// Todo: Valid terrain should be specified in the resource
-					if (!w.IsCellBuildable(new int2(x,y), false))
+					if (!AllowOreAt(new int2(x,y)))
 						continue;
 					
 					content[x, y].type = resourceTypes.FirstOrDefault(
@@ -89,6 +89,14 @@ namespace OpenRA.Traits
 					}
 		}
 
+		bool AllowOreAt( int2 a )
+		{
+			if( !world.Map.IsInMap( a.X, a.Y ) ) return false;
+			if( !world.GetTerrainInfo( a ).Buildable ) return false;
+			if( world.WorldActor.Trait<UnitInfluence>().AnyUnitsAt( a ) ) return false;
+			return true;
+		}
+
 		Sprite[] ChooseContent(ResourceType t)
 		{
 			return t.info.Sprites[world.SharedRandom.Next(t.info.Sprites.Length)];