In Mediawiki 1.3 and 1.4, you could "wipe" revision history reasonably easily. You just wipe the single MySQL table (mw_old), flush the objectcache, and previous revisions of the entire wiki were blown away. Any links into history items were dynamically rebuilt during subsequent accesses.
Is there a way to do this in 1.5.X or 1.6.X? We'd like to do this when we take sites that have been in development internally and put them into production with a "clean slate" with no trace of all of the test revisions.