Force keyring reinstall also when debian-archive-keyring is out of date

This fixes #405. When debian-archive-keyring is out of date, the errors look like this:

> W: GPG error: http://ftp.debian.org squeeze-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553
W: GPG error: http://ftp.debian.org squeeze-proposed-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553
W: GPG error: http://ftp.debian.org squeeze-lts Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553

So the forced keyring reinstall was never triggered.