support opening files of unsync repo from activity tab

![screen shot 2014-11-26 at 14 37 07](https://cloud.githubusercontent.com/assets/2123461/5197235/cd71f988-7579-11e4-9375-e0536015aac2.png)

Oh, I must make a mistake with something. There is no such a line in ``FileBrowserDialog``. Sorry for that.