[RFC] current file exists. overwrite it, or upload as an alternative name

![screen shot 2014-11-05 at 15 10 36](https://cloud.githubusercontent.com/assets/2123461/4913961/1e3325b0-64bb-11e4-89b3-c8df46b13025.png)

I think this "not not_update" is not straightforward. What about make it `bool update`, and default to false?