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/Framework/IScene.cs

@@ -63,5 +63,7 @@ namespace OpenSim.Framework
         bool PresenceChildStatus(LLUUID avatarID);
 
         string GetCapsPath(LLUUID agentId);
+
+        T RequestModuleInterface<T>();
     }
-}
+}