Bug#38127: apt: apt-get's exit code

[Roderick Schertler <roderick@argon.org>]

Package: apt
Version: 0.3.6

apt-get exits with 0 status when it has errors downloading packages.
It would be useful if it exited with a non-zero status in this case.
I think it makes sense for it to do that all the time, but if there's
some problem with doing that, it would be useful if apt-get had a switch
to get it to behave that way.