Drop support for lenny, squeeze, wheezy, jessie, stretch + buster Debian releases and default to bookworm Debian lenny (v5), squeeze (v6), wheezy (v7), jessie (v8), stretch (v9) and buster (v10) are all EOL and we don't support any of them any longer.
Drop support for Debian wheezy It's oldoldstable nowadays and we no longer use it anywhere, so let's drop related zsh completion and config files.
Provide jessie support for systemd + recent kernel packages To be able to use systemd-container we need the systemd version from jessie-backports. We also need recent versions of linux-base, firmware-misc-nonfree, firmware-linux-nonfree + firmware-linux from jessie-backports for the related kernel packages.
Fix apt 1.1 regression in apt-preferences handling apt >=1.1 fails to parse our apt-preferences setup: | E: Invalid record in the preferences file /etc/apt/preferences, no Package header
Fix creation of images based on Wheezy after the udev fix in grml-live The grml-live repo currently ships an own udev for a bugfix, which only affects Jessie and later. This version of udev is not installable in Wheezy and results in an failed image build. Let's pin udev to the Wheezy version on Wheezy, as the fix is not needed there anyways.