Show only Enabled Themes in Block Config

On the blocks configuration page (admin/build/block) menu items are created for all themes in the Drupal installation. Since it's unlikely that blocks will need to be configured for disabled themes, we should remove these items altogether when the theme is not enabled. The theme system already uses this approach for the various settings pages for themes (admin/build/themes/settings), so it seems like it's only logical to do the same for blocks.

Currently in system.module:

  foreach (list_themes() as $theme) {
    if ($theme->status) {
      $items['admin/build/themes/settings/'. $theme->name] = array(
        'title' => $theme->info['name'],
        'page arguments' => array('system_theme_settings', $theme->name),
        'type' => MENU_LOCAL_TASK,
      );
    }
  }

Currently in block.module:

  $default = variable_get('theme_default', 'garland');
  foreach (list_themes() as $key => $theme) {
    $items['admin/build/block/list/'. $key] = array(
      'title' => '!key settings',
      'title arguments' => array('!key' => $theme->info['name']),
      'page arguments' => array('block_admin_display', $key),
      'type' => $key == $default ? MENU_DEFAULT_LOCAL_TASK : MENU_LOCAL_TASK,
      'weight' => $key == $default ? -10 : 0,
    );
  }