remove unnecessary and expensive node_load() from uc_catalog_buy_it_now_form_validate()

function uc_catalog_buy_it_now_form_validate($form, &$form_state) {
  if (module_exists('uc_attribute')) {

    $node = node_load($form_state['values']['nid']); //not needed at all!

    $attributes = uc_product_get_attributes($node->nid); //nid is already in $form_state
    if (!empty($attributes)) {
      drupal_set_message(t('This product has options that need to be selected before purchase. Please select them in the form below.'), 'error');
      drupal_goto('node/'. $form_state['values']['nid']);
    }
  }
}

I've also notice there are lot of using node_load() in such simple tasks for example uc_product_is_product with 'nid' as an argument does that huge task just to check single type field. This can be done much faster, for example we can check if the following query is not empty - 'select nid from uc_products where nid='

Ubercart can be much faster...