Show git cloning root directory at settings dialog

@dinhviethoa

By the way, there's root cause. `Entry.fullpath` is not true full path.  It had returned true full path at https://github.com/dart-lang/spark/pull/1163

I'll dig into the reason about it.

This handles https://github.com/dart-lang/spark/issues/1239

![image](https://f.cloud.github.com/assets/756988/2360817/b4dfde6e-a629-11e3-9da7-f510402f7800.png)