cargo: support for actors being removed from the world, but not dying

OpenRa.Game/Actor.cs

@@ -36,6 +36,7 @@ namespace OpenRa.Game
 			Location = location;
 			CenterLocation = Traits.Util.CenterOfCell(Location);
 			Owner = owner;
+			IsInWorld = true;
 
 			if (Info == null) return;
 
@@ -123,6 +124,7 @@ namespace OpenRa.Game
 		}
 
 		public bool IsDead { get { return Health <= 0; } }
+		public bool IsInWorld { get; set; }
 
 		public DamageState GetDamageState()
 		{

OpenRa.Game/Orders/UnitOrderGenerator.cs

@@ -27,7 +27,7 @@ namespace OpenRa.Game.Orders
 
 		public void Tick()
 		{
-			selection.RemoveAll(a => a.IsDead);
+			selection.RemoveAll(a => !a.IsInWorld);
 		}
 
 		public void Render()

OpenRa.Game/World.cs

@@ -11,7 +11,10 @@ namespace OpenRa.Game
 		List<Action<World>> frameEndActions = new List<Action<World>>();
 
 		public void Add(Actor a) { actors.Add(a); ActorAdded(a); }
-		public void Remove(Actor a) { actors.Remove(a); ActorRemoved(a); }
+		public void Remove(Actor a)
+		{
+			a.IsInWorld = false; actors.Remove(a); ActorRemoved(a);
+		}
 
 		public void Add(IEffect b) { effects.Add(b); }
 		public void Remove(IEffect b) { effects.Remove(b); }