tests: new test for mq qdiff command `hg qdiff .' is supposed to work but it is currently broken. This test should help us verify when it gets fixed.

#!/bin/sh

hg init
mkfifo p

hg serve --stdio < p &
P=$!
(echo lock; echo addchangegroup; sleep 5) > p &
Q=$!
sleep 3
kill -HUP $P
wait
ls .hg