git-finish: fast-forward destination branches before merging into them

local/bin/git-finish

@@ -14,6 +14,7 @@ git checkout $branch || exit $?
 merge-into() {
 	echo "Merging $branch into $1..." >&2
 	git checkout $1 || exit $?
+	git merge --ff-only || exit $?
 	git merge --no-ff $branch --message "Merge $kind '$name'$pullreq into $1" || exit $?
 }