Doctrine File Upload example uses __DIR__

[oscargala]

One of the SensioLabs Insight checks for the use of absolute path constants like DIR and FILE.

In the Doctrine File Upload example DIR is being used:
https://github.com/symfony/symfony-docs/blob/2.4/cookbook/doctrine/file_uploads.rst

   protected function getUploadRootDir()
    {
        // the absolute directory path where uploaded
        // documents should be saved
        return __DIR__.'/../../../../web/'.$this->getUploadDir();
    }

I don't have a fix myself yet. Maybe someone else knows the best way to remove DIR from this class?

[weaverryan]

We've added a note. Really, we may just need to bite the bullet and rewrite this whole entry to use listeners, which are the better approach. See #2346

Thanks!