Form submit handler: Adds JavaScript and CSS that wasn't on the original form.
function ajax_forms_test_lazy_load_form_submit($form, &$form_state) {
if ($form_state['values']['add_files']) {
drupal_add_js(array(
'ajax_forms_test_lazy_load_form_submit' => 'executed',
), 'setting');
drupal_add_css(drupal_get_path('module', 'system') . '/system.admin.css');
drupal_add_js(drupal_get_path('module', 'system') . '/system.js');
}
$form_state['rebuild'] = TRUE;
}