Bug#248037: package-versions is extremly slow

[Petter Reinholdtsen <pere@hungry.com>]

[Colin Watson]
> grep-dctrl is your friend ...

Yet another tool I don't use very often. :)

But it does not really solve the problem I wanted to solve using
package-versions.  grep-dctrl isn't available within d-i, and I
normally use package-version from within d-i.

But I guess we can drop the call to package-version in the
prebaseconfig script, and copy the status file instead.

Also, I'll rewrite package-version to a faster version, based on
Martins ideas.