Properly clean up traits that used to hook only death.

OpenRA.Game/Actor.cs

@@ -225,6 +225,9 @@ namespace OpenRA
 				if (IsInWorld)
 					World.Remove(this);
 
+				foreach (var t in TraitsImplementing<INotifyActorDisposing>())
+					t.Disposing(this);
+
 				World.TraitDict.RemoveActor(this);
 				Disposed = true;
 

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -94,6 +94,7 @@ namespace OpenRA.Traits
 	public interface INotifyDamageStateChanged { void DamageStateChanged(Actor self, AttackInfo e); }
 	public interface INotifyRepair { void Repairing(Actor self, Actor host); }
 	public interface INotifyKilled { void Killed(Actor self, AttackInfo e); }
+	public interface INotifyActorDisposing { void Disposing(Actor self); }
 	public interface INotifyAppliedDamage { void AppliedDamage(Actor self, Actor damaged, AttackInfo e); }
 	public interface INotifyBuildComplete { void BuildingComplete(Actor self); }
 	public interface INotifyBuildingPlaced { void BuildingPlaced(Actor self); }