Log Message:
Update www/drupal6 package to 6.15, fixing security problem.

Drupal 6.15, 2009-12-16
----------------------
- Fixed security issues (Cross site scripting), see SA-CORE-2009-009.
- Fixed a variety of other bugs.

other pkgsrc changes:

* Add PKG_DESTDIR_SUPPORT spport.
* Use REPLACE_INTERPRETER.
* Change default.settings.php handling to fix PR pkg/42355.