Form validation handler for node_form().
function node_form_validate($form, &$form_state) {
// $form_state['node'] contains the actual entity being edited, but we must
// not update it with form values that have not yet been validated, so we
// create a pseudo-entity to use during validation.
$node = (object) $form_state['values'];
node_validate($node, $form, $form_state);
entity_form_field_validate('node', $form, $form_state);
}