[Raring RFC] Fix base package module dependencies

[Stefan Bader]

The bug was just about libceph but Scott (cc'd) suggested we
let the build fail if any module in the base package depends
on one only in the extras package (patch #2). It turned out
that there is already a depmod but missing modules are only
a mere warning (and we never were good at heeding warnings).

So in order to have #2 this requires a little bit more for #1.
Question is whether people caring for a small base package can
live with the additional 1.1M...

I suppose for the SRU into Q and P) we only want to add libceph
(which I would do seperately).

Oh, I test-build amd64 and i386. I was not sure whether the new
generic arm still does an extra.

-Stefan