"threads" command now works. I've added manual tracking of threads (only if compiled in DEBUG mode)... Its ugly and even requires a separate thread to track the treads, but it will be very valuable in debugging.

OpenSim/Region/Environment/Modules/XMLRPCModule.cs

@@ -584,6 +584,7 @@ namespace OpenSim.Region.Environment.Modules
                 httpThread.IsBackground = true;
                 finished = false;
                 httpThread.Start();
+                OpenSim.Framework.ThreadTracker.Add(httpThread);
 
                 return reqID;