incremental for loop

src/echo.js

@@ -10,7 +10,7 @@ window.Echo = (function (window, document, undefined) {
   };
 
   var _pollImages = function () {
-    for (var i = store.length; i--;) {
+    for (var i = 0, l = store.length; i < l; i++;) {
       var self = store[i];
       if (_inView(self)) {
         self.src = self.getAttribute('data-echo');