A user trying to upgrade from 1.2.6 reported failure of the 'redirect' table
updater script, whose second part is reading data out of 'pagelinks' and 'page'.
Since the table and field updaters are run in a batch before bigger updaters,
this seems to be running out of order; the structure migration hasn't happened
yet so there's no tables to read from.
This may break upgrades from other pre-1.4 releases as well.