Example of preprocess exclude isn't working

Hi, I've noticed a mistake in preprocess example for excluding an image from being unveiled. (unveil.example.inc).
In order to get that working, you should pass vars by reference:

function unveil_example_preprocess_image(&$vars) {
  // Some business logic for exluding an image from unveil.
  if ($vars['style_name'] == 'excluded_imagestyle') {
    // Variable denoting that this image should be excluded from
    //   being unveiled, meaning it will simply be shown on page load.
    $vars['unveil_exclude'] = TRUE;
  }
}

I know it's a minor thing and is probably an oversight, but I reckon it might save someone from a confusion.
Cheers!