Add Plug and Pluggable for building actor-specific upgrades.

OpenRA.Mods.Common/Traits/Plug.cs

@@ -0,0 +1,24 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2015 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common.Traits
+{
+	public class PlugInfo : TraitInfo<Plug>
+	{
+		[Desc("Plug type (matched against Upgrades in Pluggable)")]
+		public readonly string Type = null;
+	}
+
+	public class Plug { }
+}