title: jqgrid not work on IE8
body: <p>my below code not worked on IE 8.
  Its a JQGrid (treegrid) to display treegrid format from json server. it worked at firefox.</p>
  
  <pre><code>$(function () {
      "use strict";
      $("#tree").jqGrid({
          url: "http://myJSON-URL/",
          datatype: "json",
  
          colNames: ['id', 'Prestations'],
          colModel: [
                  { name: 'id', width: 100, key: true, hidden: true },
                  { name: 'name', width: 785, sortable: false }
              ],
          sortname: 'id',
          sortorder: "asc",
          hiddengrid: true,
          gridview: true,
          treeGrid: true,
          treeGridModel: "adjacency",
          ExpandColumn: 'name',
          ExpandColClick: true,
          jsonReader: { repeatitems: false, root: function (obj) { return obj; } },
          height: "auto"
      });
  });
  </code></pre>
  
  <p>I think its AJAX cors problem.
  Any idea? thanx.</p>
  
  <p>The json server side responsed these:</p>
  
  <pre><code> json = [
  {
      "id": "1",
      "name": "ECHANGEUR",
      "level": "0",
      "parent": "null",
      "isLeaf": false,
      "expanded": false,
      "loaded": true
  },
  {
      "id": "1_1",
      "name": "Intervention Aller sur Site",
      "level": "1",
      "parent": "1",
      "isLeaf": false,
      "expanded": false,
      "loaded": true
  },
  {
      "id": "1_1_1",
      "name": "Date et heure d'arrivée sur le site",
      "level": "2",
      "parent": "1_1",
      "isLeaf": true,
      "expanded": true,
      "loaded": true
  },
  {
      "id": "1_1_2",
      "name": "Consignation de l'échangeur",
      "level": "2",
      "parent": "1_1",
      "isLeaf": true,
      "expanded": true,
      "loaded": true
  }
  </code></pre>
  
  <p>];</p>