Add squeeze-backports to sources.list.d

[nahuel]

It will be nice to include a /etc/apt/sources.list.d/squeeze-backports.list.disabled file (and the matching one for the other debian releases) with the following content:

deb http://archive.debian.org/backports.org squeeze-backports main contrib non-free

[tianon]

Interesting idea -- I hesitate to add this to the images, especially since it's much more straightforward in newer releases (where backports live in the main archive), but more importantly because this differs from a "normal" Debian install, where I'm not aware of anything that automatically creates files like this. 😅

[nahuel]

Maybe just adding a documentation note about the backport sources for these releases will suffice, is not easy to find them (googling returns many outdated links).