spree/spree_multi_currency — pull request #22 by Bartuz (2014-06-10 15:37:23+00:00)
Title: Adds logic to swap items in cart on currency change

Actually its same code as it was pushed on 2-2-stable branch here: 977f9eb46455a943f4ce49de8cc4d6ea88f3bfce .
Surprisingly it works on 2-1-stable!