Let CreateGroup use ExtraActors field.

OpenRA.Game/Orders/UnitOrderGenerator.cs

@@ -52,10 +52,7 @@ namespace OpenRA.Orders
 
 			// HACK: This is required by the hacky player actions-per-minute calculation
 			// TODO: Reimplement APM properly and then remove this
-			yield return new Order("CreateGroup", actorsInvolved.First().Owner.PlayerActor, false)
-			{
-				TargetString = actorsInvolved.Select(a => a.ActorID).JoinWith(",")
-			};
+			yield return new Order("CreateGroup", actorsInvolved.First().Owner.PlayerActor, false, actorsInvolved.ToArray());
 
 			foreach (var o in orders)
 				yield return CheckSameOrder(o.Order, o.Trait.IssueOrder(o.Actor, o.Order, o.Target, mi.Modifiers.HasModifier(Modifiers.Shift)));