Unfilter anchor tags in source field

It's possible that recipes may need to be attributed to Internet sources. In fact, it's a requirement in my current project which employs the Recipe module. I overrode the sanitation function in my project, but other people might want to have this ability too. I'd like to add <a> to the list of unfiltered tags for the source field in recipe_node_sanitize().

Current:

  if (!empty($node->recipe_source)) {
    $node->recipe_source = filter_xss($node->recipe_source, array());
  }

Proposed:

  if (!empty($node->recipe_source)) {
    $node->recipe_source = filter_xss($node->recipe_source, array('a'));
  }

Patch to follow.