buildconfig.d/30_apt: Using short option -o instead of long option --option, because aptitude does (used by grml-debootstrap) not support that.
build-steps.d/1300_create-debian-img: added export UPGRADE_SYSTEM='no', comments
needed to move UPGRADE_SYSTEM from build-steps.d/1300_create-debian-img to grml_config
work on using frozen repository snapshot.debian.org
refactoring; fix