Support tar --auto-compress for backups.

This is the patch from Matt Barry introducing the usage of tar --auto-compress for deluser. I have refactored the patch into commits that are more to my liking. This made the commits look like they were written by me, I have tried to put Matt into the commit message for credit.

@zaharazod, is it ok for you to merge is this way or would you prefer to do some refactoring on your merge request?

Greetings Marc