A big, fat commit with a shitload of internal changes.  Not that much
visual changes:

- removed redundant files user.class.php, calendar.class.php
  and backend.class.php.
- converted *all* mysql queries to queries supported by the
  database abstraction layer.
- expanded the watchdog to record more information on what
  actually happened.
- bugfix: anonymous readers where not able to view comments.
- bugfix: anonymous readers could gain read-only access to
  the submission queue.
- bugfix: invalid includes in backend.php
- bugfix: invalid use of '$user->block'

and last but not least:

- redid 50% of the user account system