Colour Zones recalculation

[tomczak]

In Colour Zones, even if the Auto Preview is off, adjustment to the mask sliders causes instant recalculations, which makes it hard to set the sliders to the right positions (which I know more or less after probing the image).

[jsachs]

It looks like it is only recomputing the histograms and not the entire transformation -- something similar happens in some other transformations as well. It does this in case you change the Amount settings which in turn can affect the histogram.