Renders a form with a list of available database updates.
function update_selection_page() {
// Make sure there is no stale theme registry.
cache()
->deleteAll();
drupal_set_title('Drupal database update');
$elements = drupal_get_form('update_script_selection_form');
$output = drupal_render($elements);
update_task_list('select');
return $output;
}