Thanks for adding these new tests. Looking at them, I just realized how weird this line looks as part of the output from `rbenv versions`:

```
* system (set the global version with: `rbenv global VERSION`)
```

It has the asterisk, meaning it's the current version, but it also says "set the global version with…" in parentheses. It was a good idea to add this to `rbenv version` output, but in this command it just looks awkward and out of place.

So, in `versions` output, the information in the parentheses should only be shown if there was an actual origin of that version (RBENV_VERSION variable, `.ruby-version` file, global version), and there shouldn't be parentheses if "system" version was just a fallback in case the global version doesn't exist.

I think something like this would be a better output for the `versions` command. Thoughts?

```
* system
  1.8.7
  1.9.3

You don't have any Ruby version selected as the default version.
Set the default version with: `rbenv global VERSION`
```