Returns HTML for the last time we checked for update data.
In addition to properly formatting the given timestamp, this function also provides a "Check manually" link that refreshes the available update and redirects back to the same page.
$variables: An associative array containing:
theme_update_available_updates_form()
function theme_update_last_check($variables) {
$last = $variables['last'];
$output = '<div class="update checked">';
$output .= $last ? t('Last checked: @time ago', array(
'@time' => format_interval(REQUEST_TIME - $last),
)) : t('Last checked: never');
$output .= ' <span class="check-manually">(' . l(t('Check manually'), 'admin/reports/updates/check', array(
'query' => drupal_get_destination(),
)) . ')</span>';
$output .= "</div>\n";
return $output;
}