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

echo "[extensions]" >> $HGRCPATH
echo "mq=" >> $HGRCPATH

hg init a
cd a

echo 'base' > base
hg ci -Ambase -d '1 0'

hg qnew -mmqbase mqbase

hg qsave
hg qrestore 2