Please allow base-files 4.0.5 in lenny

[Santiago Vila <sanvila@unex.es>]

  * Changed awk from Depends to Pre-Depends. Closes: #314571, #469552.
    This is required to make the awk virtual package to be truly essential,
    as only essential packages, their predependencies, and the dependencies
    of their predependencies are guaranteed to be "working at all times".
    Previously, the packaging system was allowed to remove an awk flavour
    and install another one in the middle of an upgrade, which may break
    packages using awk in their preinsts (and in fact, it happened).
    Tkanks a lot to Steve Langasek for clarifying this issue.

[ Note: This change was already pre-approved by the release team ].

I'd like to see 4.0.5 in lenny before fixing #488376.

Thanks.