Fixes #53 SplFileInfo doesn't throw exception

The `_make_directory` function was failing due to an unused resource object.

Also, I couldn't find any evidence of PHP ever throwing an exception on `mkdir`, but I [left it in](https://github.com/kohana/cache/blob/3.3/master/classes/Kohana/Cache/File.php#L75-L89) just in-case.


@enov I think best if @rafi could PR this to 3.3/develop with the drupal way, and optionally once that's merged up to 3.4 we could then remove the param and conditional for neatness (though I don't think that's essential).

Also there should really be a unit test for this...