Applying patch from Gabriele Gristina <gabriele.gristina@gmail.com> to fix automated checks for using aptitude.

Some shells (like dash) will exit fatally when the shift builtin is called
beyond the last option.

Handling dist-upgrade right after bootstrap with copy of chroot_archives as bootstrap_archives in preparation for a future multi-archive bootstrap.

It is important for derivatives that the bootstrap cache is setup completely,
it is re-used in several places and thus cannot consist of the parent
distribution only.

Until there's a supportable way to bootstrap from multiple archives at the same time
(and multistrap doesn't work for that as discussed in the past), we're going to run
a lot of duplicated code here to massage the apt sources for the time being.