Delivers an "access denied" error to the browser.
Page callback functions wanting to report an "access denied" message should return MENU_ACCESS_DENIED instead of calling drupal_access_denied(). However, functions that are invoked in contexts where that return value might not bubble up to menu_execute_active_handler() should call drupal_access_denied().
function drupal_access_denied() {
drupal_deliver_page(MENU_ACCESS_DENIED);
}