The .gitattributes and .gitignore files do not need to be present in
packaged sources, as they are for people using the Git repository.
People who download tarballs usually don't reimport into Git -- they
should just download the actual repositories.

Meanwhile, the .tag file is quite useful. Instead of making Git extract
to the useless SHA-1 of the $n string, ask git-archive to store
the SHA-1 of the commit being packaged.

Change-Id: I9ebe5e6d4a854bda1191c1917eead7dde54a0e5a
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>