Menu callback: displays the 'Add new test_entity' form.
function field_test_entity_add($fttype) {
$fttype = str_replace('-', '_', $fttype);
$entity = field_test_create_entity(NULL, NULL, $fttype);
drupal_set_title(t('Create test_entity @bundle', array(
'@bundle' => $fttype,
)), PASS_THROUGH);
return entity_get_form($entity);
}