Add sensor, dataserver requests, timer and listener counts to "xengine status" command.

This is for diagnostic purposes.

OpenSim/Region/Framework/Interfaces/IWorldComm.cs

@@ -49,6 +49,11 @@ namespace OpenSim.Region.Framework.Interfaces
 
     public interface IWorldComm
     {
+        /// <summary>
+        /// Total number of listeners
+        /// </summary>
+        int ListenerCount { get; }
+
         /// <summary>
         /// Create a listen event callback with the specified filters.
         /// The parameters localID,itemID are needed to uniquely identify