Something

<?php
/**
 * Implementation of hook_form_alter().
 */
function pubrev_form_alter(&$form, $form_state, $form_id) {
  if ($form_id == 'node_form') {
    $form['options']['pubrev_allow'] = array(
      '#type' => 'checkbox',
      '#title' => t('Public revision access'),
      '#default_value' => variable_get('pubrev_allow', false),
      '#description' => t('Allow anonymous users to view the revisions of this page.'),
    );
  }
}
?>