abstract.inc etc. expected to be in PHP's include path

I installed meta tags 5.x-1.8-rc1 on a Drupal 5.7 site and got lots (well, 6) of errror messages like this:
---
warning: _nodewords_get_possible_tags(modules/nodewords/metatags/abstract.inc) [function.-nodewords-get-possible-tags]: failed to open stream: No such file or directory in /srv/www/htdocs/drupal/modules/nodewords/nodewords.module on line 730.
warning: _nodewords_get_possible_tags() [function.include]: Failed opening 'modules/nodewords/metatags/abstract.inc' for inclusion (include_path='/usr/share/php') in /srv/www/htdocs/drupal/modules/nodewords/nodewords.module on line 730.
---
A little digging around revealed that the nodewords.module code had line 730 as:

      include_once($filename);

Now, my default PHP include_path is '/usr/share/php', per the error message above. I noticed that
other Drupal calls to include_once prefixed the included filename with "./" to signify the local
directory tree.
Changing the highlighted code to

    include_once "./$filename";

removes the warning messages

I originally reported this at http://drupal.org/node/231192