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

HGRCPATH=$HGTMP/.hgrc; export HGRCPATH
echo "[extensions]" >> $HGTMP/.hgrc
echo "mq=" >> $HGTMP/.hgrc

hg init a
cd a
hg qnew first.patch
hg qnew first.patch

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

exit 0