Apply patch of latest commit in master for the dustflux output PR #420 to release1.6 branch

[jmaerz]

Hi @TomasTorsvik and @JorgSchwinger , this is the PR to replay the dustflux output commit #420 to the the release1.6 branch. I ended up using

git show HEAD > dust.patch
git apply --reject --ignore-whitespace dust.patch

which resulted in a few rejected hunks of the patch that then needed to be inserted manually. A cherrypick didn't work out for some reason.

[TomasTorsvik]

@jmaerz - Thanks! This looks fine to me.
I still don't understand why the cherry-pick option didn't work, but I suspect it has something to do with how git compares changes introduced in the release-1.6 and master branches. The git-cherry-pick documentation describes what happens when git is unable to apply changes, which is the case we have run into here.
As the master branch develops further, it will likely become increasingly difficult to rely on cherry-picking changes back to the release-1.6 branch. Since fewer changes are introduced in release-1.6, I wonder if there may be less issues in applying patches from release-1.6 to master. Maybe something to test, if we have changes in the future that we know will go into both branches.