Add a temporary workaround that partially fixes the Shift+drag problem

I still need to invent a better solution. The real problem is that for a
single settings->setPaintOpSize() we get 4 or 5
KisPaintOpConfigWidget::setConfigurationSafe() which runs quite slowly.
It seems to be reproducible on slower machines only. On Core i7 we get
exactly one setConfigurationSafe() for each setPaintOpSize() :)