Some complex re-ordering to make prebuild do what needed to be done.

It is now possible to use module interfaces without referencing Scene.
Place those interfaces in OpenSim/Region/Interfaces. They may not
use any refs from OpenSim.Region.Environment as parameters.
This resolves a circular library ref introduced in r5949

OpenSim/Region/Environment/Scenes/Scene.Inventory.cs

@@ -35,6 +35,7 @@ using libsecondlife.Packets;
 using log4net;
 using OpenSim.Framework;
 using OpenSim.Framework.Communications.Cache;
+using OpenSim.Region.Interfaces;
 using OpenSim.Region.Environment.Interfaces;
 
 namespace OpenSim.Region.Environment.Scenes

OpenSim/Region/Environment/Scenes/Scene.cs

@@ -2963,7 +2963,7 @@ namespace OpenSim.Region.Environment.Scenes
         /// For the given interface, retrieve the region module which implements it.
         /// </summary>
         /// <returns>null if there is no module implementing that interface</returns>
-        public T RequestModuleInterface<T>()
+        public override T RequestModuleInterface<T>()
         {
             if (ModuleInterfaces.ContainsKey(typeof(T)))
             {

OpenSim/Region/Environment/Scenes/SceneBase.cs

@@ -220,5 +220,10 @@ namespace OpenSim.Region.Environment.Scenes
 
             return null;
         }
+
+        public virtual T RequestModuleInterface<T>()
+        {
+            return default(T);
+        }
     }
 }