Improved cache update handling

app/index.html

@@ -59,6 +59,35 @@
   <script type="text/javascript" src="js/directives.js"></script>
   <!-- endbuild -->
 
+  <script type="text/javascript">
+  (function () {
+    if (!window.applicationCache || !window.addEventListener) {
+      return;
+    }
+    var appCache = window.applicationCache,
+        canceled = false,
+        scheduleUpdate = function () {
+          setTimeout(function () {
+            appCache.update();
+          }, 300000);
+        };
+
+    window.addEventListener('load', function(e) {
+      appCache.addEventListener('updateready', function(e) {
+        if (appCache.status == appCache.UPDATEREADY) {
+          if (!canceled && confirm('A new version of Webogram is available. Load it?')) {
+            window.location.reload();
+          } else {
+            canceled = true;
+            scheduleUpdate();
+          }
+        }
+      }, false);
+      appCache.addEventListener('noupdate', scheduleUpdate, false);
+      appCache.addEventListener('error', scheduleUpdate, false);
+    });
+  })();
+  </script>
 
 </body>
 </html>