put out full exception stack if something reaches top of base http server OnRequest() on both mono and .net

replace Newtonsoft.Json.XML since the updated copy got accidentally reverted by another commit

OpenSim/Framework/Servers/HttpServer/BaseHttpServer.cs

@@ -310,7 +310,7 @@ namespace OpenSim.Framework.Servers.HttpServer
             }
             catch (Exception e)
             {
-                m_log.ErrorFormat("[BASE HTTP SERVER]: OnRequest() failed with {0} {1}", e.Message, e.StackTrace);
+                m_log.Error(string.Format("[BASE HTTP SERVER]: OnRequest() failed with "), e);
             }
         }