Track masqueraded users when making node revisions

for anyone iterested in a working solution for that issue I added in my custom module this code:

/**
 * Implements hook_node_update().
 */
function casaconvenienza_node_update($node) {
  // When masqueraded users add new revisions the revision uid should be set to the real user's uid
  if ($node->revision && !empty($_SESSION['masquerading']) && $node->vid) {
    db_query("UPDATE {node_revision} SET uid=:uid WHERE vid=:vid",
      array(':uid' => intval($_SESSION['masquerading']), ':vid' => $node->vid));
  }
} // casaconvenienza_node_update

Altering database directly is not a good idea but AFAIK there's no hook to edit revision uid, here is the relevant node.module part in node_save() function:

      if (!empty($node->revision)) {
        _node_save_revision($node, $user->uid);
      }

The revision uid is set from current user object.