More robust node author class for styling

In template.php:

  // Add a class to allow styling based on the node author.
  $vars['attributes_array']['class'][] = drupal_html_class('author-' . $vars['node']->name);

using the user name here isn't the most robust information about the user in the case for example of a name change. It is also not friendly to methods where the obfuscating the username is wanted.

Using the user id seems like a more robust approach here, since the uid does not change unless the username.