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
hg qnew first.patch
hg qnew first.patch

touch ../first.patch
hg qimport ../first.patch

exit 0