fix a iframeUpload bug

This bug make iframeUpload always upload the first time picked file, for example: 
You open the page in a browser only support iframe upload,
first time, you want to upload 'tree.jpg', so you pick it, then 'tree.jpg' upload automatically, it's good;
after that, you want to upload 'flower.jpg', so you pick it, but the bug make 'tree.jpg' upload again. (actually you couldn't upload any other file without refresh)

Reason:
iframeUpload clone and replace the input file element with a new one, but when `change` event trigger, the `fileInput` in callback is point to the old one.