Find the system's MD5 binary. Different binaries calculate MD5 checksums on different systems. Try a couple known programs and only calculate and verify the checksum if they exist. This should silence warnings on eg OpenBSD.

#!/bin/sh

unset HGUSER
EMAIL="My Name <myname@example.com>"
export EMAIL

hg init test
cd test
touch asdf
hg add asdf
hg commit -d '1000000 0' -m commit-1
hg tip