Much better implementation of indirect painting. Adds the Alpha Darken composite op, as suggested by Ilmari Heikkinen. Currently only workingly implemented for RGBA8 and Grey8, the rest is pending. This adds correct indirect painting in the following cases:
* Paint with opacity varying according to tablet pressure (cool effect, especially with the non-first layer's composite op being set to darken alpha too)
* Paint on layer mask with indirect painting
* Paint on adjustment layer (pending actually working implementation of alpha darken on alpha colorspace)
* Paint with the brush op being different from 'Normal', on a layer that has a different from 'Normal' composite op. Or so =)
Thing that doesn't work yet: indirect painting on selections :(
Users of Krita Development Versions: beware! You will need to recompile koffice/filters/krita (and I even need to manually enter the magick dir and compile that manually) too, in case you only svn up in koffice/krita and make there. This is because the patch changes some things in, amongst others, the PaintLayer, on whose structure the filters depend.