Effect masks vs. selections and "embedded" transparency masks

[Dmitry Kazakov]

>
> Painting on filter masks works, you can test that by replacing the code in
> KisFilterMask::apply with the same code from the transparency mask. After
> doing that the filter mask works as a transparency mask (suprisingly without
> the crash from the transparency mask), so I supect that something goes wrong
> when the filter is applied.
>

Well, i'm trying to QImage::save() selection for both types of masks and
they differ. FilterMask's is fully white, Transp.Mask's is black.
I'm investigating the reason of that now.