Bug#346171: libstdc++6 loses changelog/copyright on upgrade

[Adam Conrad <adconrad@0c3.net>]

This comes from you doing your directory->symlink migration in preinst,
rather than postinst (to see an example of it being done correctly, see
openssh-server, or php4-mysql as examples).

If you migrate in preinst, you remove the directory, create the symlink,
THEN dpkg removes your package's files (dutifully following the symlink,
and removing the other package's changelog and copyright)

If you do it in postinst, this snafu doesn't occur, and the world goes
on happily able to read changelogs and licenses...

... Adam