Make IsDisabled a method on Actor.

This allows us to cache the disabled traits, which simplifies life for some callers since we relieve them of having to cache it, as well as improving perf for all IsDisabled calls.

OpenRA.Game/Actor.cs

@@ -85,6 +85,7 @@ namespace OpenRA
 
 		readonly IRenderModifier[] renderModifiers;
 		readonly IRender[] renders;
+		readonly IDisable[] disables;
 
 		internal Actor(World world, string name, TypeDictionary initDict)
 		{
@@ -128,6 +129,7 @@ namespace OpenRA
 
 			renderModifiers = TraitsImplementing<IRenderModifier>().ToArray();
 			renders = TraitsImplementing<IRender>().ToArray();
+			disables = TraitsImplementing<IDisable>().ToArray();
 		}
 
 		public void Tick()
@@ -277,6 +279,14 @@ namespace OpenRA
 			health.Value.InflictDamage(this, attacker, health.Value.MaxHP, null, true);
 		}
 
+		public bool IsDisabled()
+		{
+			foreach (var disable in disables)
+				if (disable.Disabled)
+					return true;
+			return false;
+		}
+
 		#region Scripting interface
 
 		Lazy<ScriptActorInterface> luaInterface;