Prepare removable media for offline updates

When update-notifier runs on a machine that is not connected to the internet, it currently says there might be some network problem.

This blueprint suggests to give the option to prepare some removable media (CD, USB-Disk, etc.) to fetch package lists and requested updates on (other) machines with internet access. (Even on those with other distros / OSes.) A removable package cache that can be used for multiple machines. "Download once, install many."

The simple method is to map the apt directories (config scripts, package cache, package lists, ...) to a removable medium and to copy some tools to the apt medium. These tools can then fill the medium with updated information and requested packages. By this the removable disk becomes something like an on-request-only update mirror for any apt frontend.

A shell script that modifies apt's environment variables appropriately exists as an example, and is available at: http://wiki.debian.org/AptMedium As well as some more information about the method.

(Compared to a wget script this should work for any apt frontend and update the package lists.)