update to latest debian-archive-keyring (2014.3)
create `make verify-debian-packages` to check commited .debs

This adds a target to check the .deb files included in this git against
what is on the Debian mirrors.
download keyring from snapshot.debian.org in case the version gets bumped

snapsnot.debian.org keeps archived versions of old packages, while the
mirrors do not.  So if a new package gets released, then 2014.3 will
disappear from the mirrors, but still be available on snapshot.debian.org
REBASE create `make verify-debian-packages` to check commited .debs