Fwd: composite_copy

[Lukast dev]

> It is also instantiated in the AddGeneralOps, however Copy2 is marked a
> userVisible = false. I think it was considered useless for users.

It was created specially so that we mix also alpha when smudging in
the original
smudge brush. When using with Pixel brush, it copied the mask exactly, so Sven
disabled it as useless (for pixel brush it was). It was whitelisted
for some paintops
like deform or smudge. I will need to check if it is still whitelisted
composite op.