Replay stuff.

FYI: Don't try to replay a game where you built any vehicles. It WILL fail horribly.

OpenRa.Game/World.cs

@@ -13,15 +13,15 @@ namespace OpenRa.Game
 		int lastTime = Environment.TickCount;
 		const int timestep = 40;
 
-		public void Add(Actor a) { actors.Add(a); ActorAdded(a); }
+		public void Add(Actor a) { actors.Add(a); ActorAdded(a); }
 		public void Remove(Actor a) { actors.Remove(a); ActorRemoved(a); }
 
-		public void Add(IEffect b) { effects.Add(b); }
+		public void Add(IEffect b) { effects.Add(b); }
 		public void Remove(IEffect b) { effects.Remove(b); }
 
 		public void AddFrameEndTask( Action<World> a ) { frameEndActions.Add( a ); }
 
-		public event Action<Actor> ActorAdded = _ => { };
+		public event Action<Actor> ActorAdded = _ => { };
 		public event Action<Actor> ActorRemoved = a => { a.Health = 0; };		/* make sure everyone sees it as dead */
 
 		public void ResetTimer()
@@ -32,16 +32,16 @@ namespace OpenRa.Game
 		public void Update()
 		{
 			int t = Environment.TickCount;
-			int dt = t - lastTime;
-			if (dt >= timestep)
-			{
-				lastTime += timestep;
-
-				foreach (var a in actors) a.Tick();
-				foreach (var e in effects) e.Tick();
-
-				Renderer.waterFrame += 0.00125f * timestep;
-				Game.viewport.Tick();
+			int dt = t - lastTime;
+			if (dt >= timestep)
+			{
+				lastTime += timestep;
+
+				foreach (var a in actors) a.Tick();
+				foreach (var e in effects) e.Tick();
+
+				Renderer.waterFrame += 0.00125f * timestep;
+				Game.viewport.Tick();
 			}
 
 			foreach (Action<World> a in frameEndActions) a(this);
@@ -49,6 +49,12 @@ namespace OpenRa.Game
 		}
 
 		public IEnumerable<Actor> Actors { get { return actors; } }
-		public IEnumerable<IEffect> Effects { get { return effects; } }
+		public IEnumerable<IEffect> Effects { get { return effects; } }
+
+		uint nextAID = 0;
+		internal uint NextAID()
+		{
+			return nextAID++;
+		}
 	}
 }