Backed out changeset 7a58581d842c This changeset breaks a number of CW tests, which depends on pre add hooks. I'm backing it out, so that we can start the need-for-speed sprint with green tests (and possibly rework this changeset)

if repo.system_source.dbdriver == 'postgres':
    sql('ALTER TABLE appears ADD COLUMN weight float')
    sql('UPDATE appears SET weight=1.0 ')