Use unsigned version format. This way can use one additional bit, and when encountering invalid revlogs with the first bit set don't produce python warnings or strange error messages.

#!/bin/sh

echo 'syntax error' > badext.py
abspath=`pwd`/badext.py

echo '[extensions]' >> $HGRCPATH
echo "badext = $abspath" >> $HGRCPATH

hg -q help help