Maybe add support for sites that reload the "express checkout page" (ie for language switches)

[iverok]

The method Vipps::vipps_buy_product which shows the page for single-product express checkout has the following code:

$session->set('__vipps_buy_product', false); // Reloads won't work but that's ok.

It turns out that's not always ok, because some multilingual plugins actually reload this page (to switch languages for example).

The deletion here is intended to make cross-site-stuff harder to do, but it isn't 100% clear it is neccessary here, and it may be easier to remove this restriction than to try to fix this in the other plugins.

[iverok]

Keeping this for now to avoid page reloads.