added Shroud.Explore overload in prep for spyplane

OpenRa.Game/Shroud.cs

@@ -79,11 +79,9 @@ namespace OpenRa
 			return IsExplored(x,y);
 		}
 
-		public void Explore(Actor a)
+		public void Explore(World w, int2 center, int range)
 		{
-			foreach (var t in a.World.FindTilesInCircle(
-				(1f / Game.CellSize * a.CenterLocation).ToInt2(), 
-				a.Info.Traits.Get<OwnedActorInfo>().Sight))
+			foreach (var t in w.FindTilesInCircle(center, range))
 			{
 				explored[t.X, t.Y] = true;
 				gapField[t.X, t.Y] = 0;
@@ -91,6 +89,13 @@ namespace OpenRa
 			dirty = true;
 		}
 		
+		public void Explore(Actor a)
+		{
+			Explore(a.World,
+				(1f / Game.CellSize * a.CenterLocation).ToInt2(), 
+				a.Info.Traits.Get<OwnedActorInfo>().Sight);
+		}
+
 		static readonly byte[][] SpecialShroudTiles =
 		{
 			new byte[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 },