Upgrade from old release fails in Drush

When upgrading from 2.2.8 to 3.4.x (/branches/3.4.arms circa 34364) via drush, the civicrm backend settings fail to load due to a SQL error:

Unknown column 'locale_custom_strings' in 'field list'
(full error attached)

I initially worked around it by commenting-out the lines from r32664 (CRM-7596), but that seemed drastic.

It turns out this particular error only affects drush upgrades – not the web-based upgrade. The discrepancy appears because CRM_Core_BAO_Settings::retrieve activates special behavior when the request path is "civicrm/upgrade". The attached patch enables drush to use the same special behavior.

(Aside: the relevant column, locale_custom_strings, was added in 3.2.alpha3; this issue most likely affects drush upgrades on any sites which predate 3.2.alph3.)