#
. git-sh-setup-script || die "Not a git archive"
-head=$(git-rev-parse --revs-only "$1")
-merge=$(git-rev-parse --revs-only "$2")
+head=$(git-rev-parse --verify "$1"^0) || exit
+merge=$(git-rev-parse --verify "$2"^0) || exit
merge_msg="$3"
dropheads() {