History: Mods clean structure

            Temporary batch to clean improper position number in the structure.

Problem: Structure numbers shown in page view can be wrong - dur of a non linear numbering in the database.

* Installation: put the batch in the tikiwiki root - after use, better to move or delete the script
*  __Dump your database - just in case__
* Run the script from the brower
** http://yoursite.com/batch_clean_structure.php?page_ref_id=x where x if the id of the structure
** http://yoursite.com/batch_clean_structure.php to clean all the structures
* Move or remove the script from the tikiroot