Committing the interface change and the addition to the modules to get

the ball rolling on replacable modules. No user functionality yet

OpenSim/Client/Linden/LLClientStackModule.cs

@@ -110,6 +110,11 @@ namespace OpenSim.Client.Linden
 
         }
 
+        public Type ReplacableInterface 
+        {
+            get { return null; }
+        }
+
         public string Name
         {
             get { return "LLClientStackModule"; }