Use document.getElementById in examples.

Previously examples would either use the now deprecated `window.$` or the
non-API-method `OpenLayers.Util.getElement`. This was well caught by @probins
and @elemoine.

examples/game-accel-ball.html

@@ -33,10 +33,9 @@
             vlayer.drawFeature(feature);
         }
         function init() {
-            var $ = OpenLayers.Util.getElement;
             map = new OpenLayers.Map( 'map', 
                 {
-                 'maxExtent': new OpenLayers.Bounds(0, 0, $("map").clientWidth, $("map").clientHeight), 
+                 'maxExtent': new OpenLayers.Bounds(0, 0, document.getElementById("map").clientWidth, document.getElementById("map").clientHeight), 
                  controls: [], 
                  maxResolution: 'auto'} 
             );