Added new Forum/Int/Anon conversions based on encryption.
Finished infrastructure for Forum ID scheme. New functions: idInt2Forum() goes from user_int_id to forum_id. idForum2Int() reverses idInt2Forum(), and idForum2Anon() does the obvious. Updated scripts/README.txt. Still work to do there. Left to do: make forum populating code use the new Forum uids.