title: Datatables ajax request not working with xhr but with local json file
body: <p>I'm using a static .json file to load a table during testing. This works fine with the following controller code:</p>
  
  <pre class="lang-js prettyprint-override"><code> function dashboardResearchPubCtrl($scope, $http, dataService, DTOptionsBuilder, DTColumnBuilder) {
      var vm = this;
      vm.dtInstance = {};
            vm.dtOptions = DTOptionsBuilder.newOptions()
      .withOption('ajax', {
          "contentType": "application/json; charset=utf-8",
          dataType: "json",
          "url": "/api/research-pub.json",
          "type": "GET",
          "data": function ( d ) {
              return JSON.stringify(d);
          }
      })
      .withOption('processing', true)
      .withOption('serverSide', true)
      .withOption('filter', false)
      .withOption('fnPreDrawCallback', function () {
          $("#overlay").show();
      })
      .withOption('fnDrawCallback', function () {
          $("#overlay").hide();
      })
      .withPaginationType('full_numbers');
  vm.dtColumns = [
      DTColumnBuilder.newColumn('content_id').withTitle('Id'),
      DTColumnBuilder.newColumn('content_title').withTitle('Title')
        ];
   }
  </code></pre>
  
  <p>However, if I change the url from "url": "/api/research-pub.json" (a local .json file) to  "url": "/api/research-pub" (the xhr endpoint (which renders the same json as the file), then datatables load the data, but instead I get the datatables warning alert message: table_id=dataTable Datatables warning: Requested unknown parameter for id 'content_id'... Chrome network shows the xhr response data, but nothing shows up in datatables. </p>
  
  <p>Is there a parameter I need to add or remove to get the xhr working? Thanks!</p>
  
  <p>This is the view code:</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;div ng-controller="dashboardResearchPubCtrl as vm"&gt;
      &lt;table id="dataTable" datatable="" dt-instance="vm.dtInstance" dt-options="vm.dtOptions" dt-columns="vm.dtColumns" class="table table-striped table-bordered table-hover dataTable"&gt;&lt;/table&gt;
   &lt;/div&gt;
  </code></pre>
  
  <p>and json response:</p>
  
  <pre class="lang-json prettyprint-override"><code>[[{"rating_cnt":140,"rating_avg":4,"content_id":"122","content_title":"Business-Driven Dealer Training","content_metadata":null,"access_level":"Member","industry":"Automotive","audience_level":"Intermediate","publish_date":"2007-01-24T00:00:00.000Z"},
      {"rating_cnt":350,"rating_avg":4,"content_id":"100","content_title":"HR Training &amp; Assessment","content_metadata":null,"access_level":"Member","industry":"Aerospace","audience_level":"Beginner","publish_date":"2014-11-14T00:00:00.000Z"}
  ]]
  </code></pre>