extra source references (Built-Using) in wheezy, britney and cd images

[Ansgar Burchardt <ansgar@debian.org>]

Hi,

sometime ago we introduces the Built-Using field to reference extra
source packages that were used to build a binary package[1].  dak
ensures these are in the archive, but doesn't require that they are in
any suite (ie. it keeps the files even though they might not be
referenced in any Sources index).

  [1] <http://bugs.debian.org/641153>

I proposed to change this so packages referenced by Built-Using are also
referenced by Built-Using[2], but haven't done much for this.  It should
be a fairly simple change on the dak-side, but more work might be
required for britney[3].

  [2] <http://bugs.debian.org/657212>
  [3] <http://bugs.debian.org/661078>

However I forgot about CD images.  These also need to include the
referenced sources so we provide the complete source on them, but
currently include only those source packages referenced in Sources.
So we should probably work on dak and britney to support including them.

An alternative would be an extra index for the additional source
packages, but this means we would need to make apt, debmirror, debian-cd
and probably others aware of them instead of just dak and britney.

Ansgar