Decouple revision.rev_id from text.old_id

Decouple revision.rev_id from text.old_id
* This will allow the backend text storage to use different id numbers
* Revisions noting metadata changes can be added to history without duplicating text
  (implemented for page move)

This changes the revision table schema and requires running update.php
or maintenance/archives/patch-rev_text_id.sql on existing test wikis.
PostgreSQL table defs are still not in sync, so not updated.