Fix and improve custom rule detection.

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -319,6 +319,7 @@ namespace OpenRA.Traits
 	public interface ITraitInfo : ITraitInfoInterface { object Create(ActorInitializer init); }
 
 	public class TraitInfo<T> : ITraitInfo where T : new() { public virtual object Create(ActorInitializer init) { return new T(); } }
+	public interface ILobbyCustomRulesIgnore { }
 
 	[SuppressMessage("StyleCop.CSharp.NamingRules", "SA1302:InterfaceNamesMustBeginWithI", Justification = "Not a real interface, but more like a tag.")]
 	public interface Requires<T> where T : class, ITraitInfoInterface { }