title: model.fetch always going to error callback
body: <pre><code>var mdl = Backbone.Model.extend({
              defaults:{
                  url:'/displayPostVariables.php',
                  age:0
              },
              initialize:function(opt){                   
                  this.url = function (){
                      return opt.url
                  }
              }
          })
          mdli = new mdl({
              'name' :'rajkamal'
          })
  
          jQuery.ajaxSetup({
              'beforeSend': function(xhr) {
                  xhr.setRequestHeader("Accept", "text/html")
              }
          })
          mdli.fetch({
              success : successcallback,
              error:errorcallback
  
          });
  </code></pre>
  
  <p>Ajax call is going but, always ends up with the error callback.
  Looks like this post <a href="https://stackoverflow.com/questions/6836433/model-fetch-success-callback-does-not-fire-on-firefox-but-works-on-chrome">model.fetch success callback does not fire on firefox, but works on chrome</a> but there is no javascript code in that.</p>
  
  <p>Thanks.</p>