title: Google maps cluster IE8 issues
body: <p>The below code works fine on firefox and IE9, but having issue updating the markers on IE8. i get  "SCRIPT16389: Unspecified error. main.js, line 20 character 313" and the markers once crated are not updating with the new set of data</p>
  
  <p>my newdata.json format is</p>
  
  <pre><code> {
      "points": [
          {
              "lat": "-28.0000",
              "long": "133.1500",
              "id": 0
          },
          {
              "lat": "-28.4710",
              "long": "153.3443",
              "id": 1
          }
      ]
  }
  </code></pre>
  
  <p>and below is the script to get the json and use clustering to display the points</p>
  
  <pre><code>var map=null;
  var markersArray = [];
  var markerCluster= null;
  google.load('maps', '3', {
          other_params: 'sensor=true'
  });
  google.setOnLoadCallback(initialize);
  
  function initialize() {
      var mapcentre = new google.maps.LatLng(-29,135);
      var mapOptions = {
          zoom: 5,
          center: mapcentre,
          mapTypeId: google.maps.MapTypeId.ROADMAP
      };
      map = new google.maps.Map(document.getElementById('map'), mapOptions);
      startTimer();
  }
  
  function startTimer(){
      setInterval(function() {
          deleteOverlays();//should delete any existing point and clear the cluster
          addMarker();
      },3000);
  }
  
  function addMarker() {
          $.ajax({
              type: "GET",
              url: "newdata.json",
              async: false,
              dataType: "json",
              success: function(data){
                  for (var i = 0, dataPoint; dataPoint = data.points[i]; i++) {
                      var latLng = new google.maps.LatLng(dataPoint.lat,dataPoint.long);
                      var marker = new google.maps.Marker({
                              position: latLng
                      });
                      markersArray.push(marker);
                  }           
  
                  markerCluster = new MarkerClusterer(map, markersArray);
              } 
  
  
          });
  }
  
  
  // Deletes all markers in the array by removing references to them
  function deleteOverlays() {
    if (markersArray.length &gt; 0) {
      for (i in markersArray) {
        markersArray[i].setMap(null);
      }
      markersArray.length = 0;
    }
    if(markerCluster!= null) {
         markerCluster.clearMarkers();
    }
  }
  </code></pre>
  
  <p>on IE8 the maps loads fine and the intial data is displaying fine, but the new data is not updated so i guess something wrong with deleteOverlays ?</p>
  
  <p>the above example is based on <a href="http://google-maps-utility-library-v3.googlecode.com/svn/trunk/markerclusterer/examples/advanced_example.html?compiled" rel="nofollow">http://google-maps-utility-library-v3.googlecode.com/svn/trunk/markerclusterer/examples/advanced_example.html?compiled</a> </p>