if rename of file fails, the rename is undone in the view - fix 2820

I've just reformat the ajax call and add the async option.

fix 2820

@Kondou-ger @tanghus Something weird happens: If the error dialog shows up, the "Ok" button doesn't work anymore. 

```
Uncaught Error: cannot call methods on dialog prior to initialization; attempted to call method 'close' jquery-1.7.2.min.js:2
e.extend.error jquery-1.7.2.min.js:2
(anonymous function) jquery-ui-1.10.0.custom.js:491
e.extend.each jquery-1.7.2.min.js:2
e.fn.e.each jquery-1.7.2.min.js:2
$.widget.bridge.$.fn.(anonymous function) jquery-ui-1.10.0.custom.js:487
functionToCall oc-dialogs.js:234
$.widget._createButtons.$.each.props.click jquery-ui-1.10.0.custom.js:9194
f.event.dispatch jquery-1.7.2.min.js:3
f.event.add.h.handle.i jquery-1.7.2.min.js:3
```

The "Close" button works as expected.