Fix the examples that used our '$' method.

examples/strategy-cluster-threshold.html

@@ -18,6 +18,7 @@
         </style>
         <script src="../lib/OpenLayers.js"></script>
         <script type="text/javascript">
+            var $ = OpenLayers.Util.getElement;
 
             // create a semi-random grid of features to be clustered
             var dx = 3;