Disable autovacuum, because we don't want it to run against
intentionally corrupted tables. Also, before corrupting the tables,
run pg_amcheck and ensure that it passes. Otherwise, if something
unexpected happens when we check the corrupted tables, it's not so
clear whether it would have also happened before we corrupted
them.

Mark Dilger

Discussion: http://postgr.es/m/AA5506CE-7D2A-42E4-A51D-358635E3722D@enterprisedb.com