Bug#680613: libav: Multi-Arch: foreign libraries

[Fabian Greffrath]

> To recap, what's the problem now?

Reinhard, I think I got it:

Imagine you have an amd64 system and have libavformat53:amd64 installed.
Now you want to install program:i386, which depends on
"libavformat-extra-53 | libavformat53". Because the former is Arch:all and
Multi-arch: foreign it is satisfying this dependency for every
architecture and it only pulls in libavformat53, which in turn is already
installed in the native architecture, i.e. libavformat53:amd64. Thus,
libavformat53:i386 is never installed and program:i386 fails to start.