Added IRegionCreator interface that all ApplicationPlugins that are creators of Scenes should implement and register with the ApplicationRegistry.StackModuleInterface<>(); So that other plugins can attach to their OnNewRegionCreated event.

Made some changes to IRegistryCore and RegistryCore so they support "Stacked" interfaces.

OpenSim/Framework/IRegistryCore.cs

@@ -4,10 +4,13 @@ using System.Text;
 
 namespace OpenSim.Framework
 {
-    public interface IRegistryCore
+    public interface IRegistryCore 
     {
         T Get<T>();
         void RegisterInterface<T>(T iface);
         bool TryGet<T>(out T iface);
+
+        void StackModuleInterface<M>(M mod);
+        T[] RequestModuleInterfaces<T>();
     }
 }