Remove the functionality allowing users to change the default direction; this is...

Remove the functionality allowing users to change the default direction; this is basically redundant with first/last.  Uncomment the multiple-ordering stuff in Pager.php, since it works fine, but comment it out in SpecialCategories.php, since the index is not unique and it won't sort correctly.  IndexPager needs to support multiple-column sort, and the index should be extended to (cat_pages, cat_title).