Allow to specify whether an upscaling of images should be done

The option is currently hidden as up to now only Nuno requested it,
but it seems to be urgent: "my icon making productivity has drop subtantialy"
((c) 2012 Nuno)

As I don't want to get blamed for an outdated Oxygen-icon-set I have
no other choice ;-)

CCMAIL: nuno.pinheiro@kdab.com