title: jQuery jsonrpc 2.0 call via .ajax() gets correct response but does not work?
body: <p>A jsonrpc 2.0 call via jquery to a Tornado web server gets a 
  "200 OK" http response and my network sniffer shows the decoded
  response as containing </p>
  
  <p><strong>{"jsonrpc":"2.0","error":null,"result":3500,"id":"jsonrpc"}</strong> </p>
  
  <p>i.e a valid jsonrpc 2.0 response. 3500 is also the correct result, 
  the RPC was to a simple add function. </p>
  
  <p>However firebug does not show response and .ajax <strong>success</strong> callback
  is not triggered. The .ajax() <strong>error</strong> and <strong>complete</strong> callbacks are
  triggered but give me no clue as to the problem. Here is the
  index.html that triggers the ajax() call. </p>
  
  <pre><code>    $(document).ready(function(){
         $.ajax({
            url: 'http://localhost:8080', 
            data: JSON.stringify ({jsonrpc:'2.0',method:'add', params:[1400,2100],id:"jsonrpc"} ),  // id is needed !!
            type:"POST",
            dataType:"json",
            success: function (result) { 
                   alert("ok");
            },
            error: function (err,status,thrown) {
                   alert ("this syntax sucks!! " + " ERROR: " + err + " STATUS: " + status + " " + thrown );
            },
            complete: function (xhr,status) { 
                   alert('Complete=&gt;  showing status as: '+ status); 
                   data = $.parseJSON(xhr.responseText);  
                   alert (data);
            } 
         });
      });
  </code></pre>