They are all installed with executable permissions in the root file
system so there is no need to have them on the scripts in that are
kept in the repository.
Removal of the package index files, aka lists, is something that needs
to be done explicitly. Doing so at `APT::Update::Post-Invoke` defeats
the purpose of running `apt-get update` in the first place.
This integrates a custom script into the APT configuration. That same
script is also run during the bootstrap. A second custom script takes
care of the integration and removes itself when done.
Complements 13f84159.
Olaf Meeuwissen