Add Thread.ResetAbort() to various thread loops to clean up errors on

shutdown. Fixes Mantis #8494.

Threads are aborted when shutting down and ThreadAbortException is odd
in that it is rethrown at the end of the catch unless the abort is
reset. No functional changes but fewer error messages on shutdown.

OpenSim/Region/ScriptEngine/Shared/Api/Implementation/AsyncCommandManager.cs

@@ -221,7 +221,8 @@ namespace OpenSim.Region.ScriptEngine.Shared.Api
         /// </summary>
         private static void CmdHandlerThreadLoop()
         {
-            while (true)
+            bool running = true;
+            while (running)
             {
                 try
                 {
@@ -230,7 +231,11 @@ namespace OpenSim.Region.ScriptEngine.Shared.Api
                     DoOneCmdHandlerPass();
                     Watchdog.UpdateThread();
                 }
-                catch ( System.Threading.ThreadAbortException) { }
+                catch ( System.Threading.ThreadAbortException)
+                {
+                    Thread.ResetAbort();
+                    running = false;
+                }
                 catch (Exception e)
                 {
                     m_log.Error("[ASYNC COMMAND MANAGER]: Exception in command handler pass: ", e);