The .gitattributes, .gitignore, .commit-template 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 "$Id$\n" string, ask git-archive to store
the SHA-1 of the commit being packaged.

Change-Id: I4ad0ed39c84555447161511f257f7768d38d2173
Reviewed-by: Christian Stromme <christian.stromme@digia.com>