Handle backslash issue

## Path manipuration(Handle backslash issue)

When `ghq.root` is given by slash-separated string, it doesn't match any files on windows. So it makes too slowly. below is a patch to call Clean(FromSlash). And convert from backslash. This should NOT affect to another platform's behavior.

Just now, ghq works on windows. yay!

## Command Behavior

Run command prompt on windows.