Add an extension to allow registering multiple interfaces of a type with

Scene. Make the script engines check that the engine name in the
//Engine:language comment is a valid engine and treat it as a normal
comment if it's not.
//DotNetEngine: needs to be written as //ScriptEngine.DotNetEngine: now, since
that is it's real internal name. //XEngine: still works

OpenSim/Framework/IScene.cs

@@ -65,5 +65,6 @@ namespace OpenSim.Framework
         string GetCapsPath(UUID agentId);
 
         T RequestModuleInterface<T>();
+        T[] RequestModuleInterfaces<T>();
     }
 }