Bingo! This fixed the problem. Now the contours of the fill zone look
much nicer (smoother). I think we still miss the trimming of spurs to
make it really good for practical etching at least with hobbyist means.
Those spurs occur wherever the fill zone gets too thin, say smaller
that the track width. I couldn't find a way to make it happen, it looks
more complicated.
I will post before/after results so you'll be able to check for
yourselves if it is an improvement or not. Then I could ask to
integrate it in one of the next releases.
