On startup, start scenes after we're set up all local scenes, rather than starting scenes before others have been created.

This aims to avoid a race condition where scenes could look to inform neighbours that they were up before those neighbours had been created.
http://opensimulator.org/mantis/view.php?id=6618

OpenSim/Framework/IScene.cs

@@ -136,5 +136,10 @@ namespace OpenSim.Framework
         ISceneObject DeserializeObject(string representation);
 
         bool CheckClient(UUID agentID, System.Net.IPEndPoint ep);
+
+        /// <summary>
+        /// Start the scene and associated scripts within it.
+        /// </summary>
+        void Start();
     }
-}
+}