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

mkdir t
cd t
hg init
echo a > a
hg add a
hg commit -m "test" -d "1000000 0"
hg verify
hg parents
hg status
hg rollback
hg verify
hg parents
hg status