Path::isLocal for stream wrappers like phar://

Theoretical question:

I think ...

``` php
Path::isLocal('phar://C:/Documents/projects/my-project.phar/composer.json');
```

... returns `false`.

Does that make sense?

The basic question here is:
How is "local" defined? Are stream wrappers to local files considered local or not?

@webmozart what do you think?
