Sweet function for getting the revision list of an entity of a given type.

get_revision_list.php

<?php
/**
 * Get a revision id list for a particular entity.
 */
function _get_entity_revision_list($type, $entity) {
  $info = entity_get_info($type);
  if (!isset($info['revision table'])) {
    // If this entity does not track revisions then return FALSE.
    return FALSE;
  }
  if (!isset($info['entity keys']['revision'])) {
    // If for whatever reason a revision table was defined, but no revision key
    // then also return FALSE.
    return FALSE;
  }
  $revisions = db_select($info['revision table'], 'r')
    ->fields('r', array($info['entity keys']['revision']))
    ->condition($info['entity keys']['id'], $entity->{$info['entity keys']['id']})
    ->execute()
    ->fetchAllAssoc($info['entity keys']['revision']);
  return array_keys($revisions);
}