Issues with Multi-Arch:same packages on purge

[Guillem Jover <guillem@debian.org>]

Hi!

[ Seems I lost track of this issue... trying to correct it now. ]

While dealing with #682365, Jonathan noticed that several packages [P]
were handling non-dpkg tracked files incorrectly on purge.

[P] <http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=682365#29>

The problem is that they might not take into account multiple package
instances from dpkg-related commands (something I warned in [W]), they
are just not doing manual file ref-counting which I think I mentioned
in the long ref-counting thread on debian-devel, or other invoked
command are not taking multiarch into account.

[W] <https://lists.debian.org/debian-devel-announce/2012/03/msg00005.html>

In any case, for some packages this might just mean that things like
caches are unnecessarily removed; but for others, important data, config
files or similar needed stuff might get removed on purge which might
render the package unusable, or might destroy user changes. Please
review your M-A:same packages.

I guess a way to detect those could be piuparts runs that install
multiple instances of Multi-Arch:same packages, purge just one of
them, and compare that the packages created by the first instance
are not removed, and that other files do not get modified. Andreas,
would that be possible?

Thanks,
Guillem