Don't unpack the upstream .git repository.

Starting with Bugzilla 4.4.7, the distributed tar files include a .git
directory. Needless to say, unpacking that on top of our own .git
directory results in chaos (including a changed "git remote" URL for
origin).  Exlude the .git directory.

The downside of this is that the pristine-tar diff file will be fairly
large.

import-upstream

@@ -37,7 +37,7 @@ fi
 
 git rm -rf --ignore-unmatch . || exit 1
 git clean -d -f -x || exit 1
-tar --strip-components=1 -x -f $tarfile || exit 1
+tar --strip-components=1 -x --exclude .git -f $tarfile || exit 1
 git add -f -A -- . || exit 1
 git commit -m"Imported Bugzilla $version." || exit 1
 git tag bugzilla-$version || exit 1