Handling of aborted downloads in retrieve

I think it might be useful to have a handling of cancelled downloads of real data from irods with km3pipe retrieve. If it is cancelled the file is not usable. And if you try to download it again it will not initiate but think the file is already there. Only deleting the link doesnt help of course.

So, I propose to have something like: if aborted then delete half written file + link again.