Implements hook_template_preprocess_default_variables_alter().
function user_template_preprocess_default_variables_alter(&$variables) {
global $user;
$variables['user'] = clone $user;
// Remove password and session IDs, since themes should not need nor see them.
unset($variables['user']->pass, $variables['user']->sid, $variables['user']->ssid);
$variables['is_admin'] = user_access('access administration pages');
$variables['logged_in'] = $user->uid > 0;
}