Add ActorInfo.HasTraitInfo<T>() requiring ITraitInfo types

OpenRA.Game/GameRules/ActorInfo.cs

@@ -183,5 +183,7 @@ namespace OpenRA
 				i => Pair.New(
 					i.Name.Replace("Init", ""), i));
 		}
+
+		public bool HasTraitInfo<T>() where T : ITraitInfo { return Traits.Contains<T>(); }
 	}
 }