Form submission handler for the 'Save and add fields' button.
field_ui_form_node_type_form_alter()
function field_ui_form_node_type_form_submit($form, &$form_state) {
if ($form_state['triggering_element']['#parents'][0] === 'save_continue') {
$form_state['redirect'] = _field_ui_bundle_admin_path('node', $form_state['values']['type']) . '/fields';
}
}