Prevent unlikely scenario bug. upay knows about postback, but settings has it not to do postback.

on third party upay settings .. user checks settings to do postback and supplies right postback page.
on drupal upay settings .. user checks settings not do any post back.

-- customer goes through the payment flow , 3rd party upay does a postback, drupal upay receives postback and processes.
-- customer gets redirected back on a non-post back settings success-link .. with the assumption that this is not a postback scenario and does the processing again.

this scenario has the payment processing done twiced.

-- need to prevent this unlikely scenario.. oh the joy.