/**
 * Override or insert variables into all templates.
 *
 * @param $variables
 *   An array of variables to pass to the theme template.
 * @param $hook
 *   The name of the template being rendered (name of the .tpl.php file.)
 */
function THEME_preprocess(&$vars, $hook) {

  // Any additional contextual link types must be added to this array.
  $keys = array(
    'block_classes',
    'node_classes',
    'page_classes',

    // Zen does not override user-profile.tpl.php.
    'user_classes',
    'views_classes',
  );

  foreach ($keys as $key) {
    if (array_key_exists($key, $vars)) {
      $vars['classes_array'][] = $vars[$key];
      unset($vars[$key]);
    }
  }
}