Add .tag file and the git-archive export options

The .gitattributes and .gitignore files do not need to be present in
packaged sources, as they are for people using the Git repository.

Change-Id: I0c9cd62fae0c4f4ca75552cbac966e27cadac45d
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>