dmapi: digitally sign release tags

Arrange for the commit marking a new release to include a
"Signed-off-by" line, and have the corresponding tag include
a digital signature.

Signed-off-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/release.sh b/release.sh
index e8b8421..0953b0d 100755
--- a/release.sh
+++ b/release.sh
@@ -13,10 +13,10 @@
 	mv doc/CHANGES.tmp doc/CHANGES
 
 echo "Commiting CHANGES update to git"
-git-commit -a -m "${version} release"
+git-commit -s -a -m "${version} release"
 
 echo "Tagging git repository"
-git-tag v${version}
+git tag -s -a -m "${version} release" v${version}
 
 echo "Creating source tarball in build/tar/"
 ./Makepkgs