usermanual: on the slideshow view
make the colorpicker symbol in parametric masks reasonably sized
Add check for bad 4th channel (alpha) values (0< || >1) to -d nan
demosaic might receive such output buffer, that was not memset'ed
First 3 channels are ok - they have just been interpolated
So we just need to make sure that 4th channel has reasonable values - let's set it to 0.0f
Force copying alpha from input buffer after LCMS calls

Apparently LCMS puts garbage into 4th channel. FIXME: is there another, better way?
Tune gamutchech - was partially broken by bad alpha in 05a558e474897293f9e36f64eb629687fcebccef