* Use Maintenance::runChild() to get the child script instance

* Use Maintenance::runChild() to get the child script instance
* Moved do_stats_init() to DatabaseUpdater and call it from doUpdates() for consistency with purgeCache(), this inverts the order of execution with default messages deletion, but I don't think this should break anything
* Removed the early return for postgres, which was a leftover from the old do_postgres_updates() crap