Check for parent/mod as well as parent.mod in findext. Debian/Ubuntu ship a system-wide hgrc that loads extensions using the syntax hgext/extension=, rather than hgext.extension=. Although the extensions work correctly, hg help <extension> doesn't understand this form without this patch.

#!/bin/sh

set -e

mkdir test
cd test
echo foo>foo
hg init
hg addremove
hg commit -m "1"
hg verify

hg clone . ../branch
cd ../branch
hg co
echo bar>>foo
hg commit -m "2"

cd ../test
hg pull ../branch
hg verify
hg co
cat foo
hg manifest