D6 code cleanup

Attached patch

• Resets CVS Id tag to blank
• adds @file comment block
• moves copyright to Doxygen @copyright
• adds standard comment blocks for hooks
• changes tab indenting to spaces
• removes t() from menu hook strings
• removes $items initializer to be consistent with the settings function not initializing $form
• initializes an unset variable $extra_cond when $mode is set on the delete query in cron