fix changenav for maxchanges != 10 for maxchanges = 25 the changelog navigation had a minimum stepsize of 30; try to calculate more useful navigation steps

#!/bin/sh

hg init
mkfifo p

hg serve --stdio < p &
P=$!
(echo lock; echo addchangegroup; sleep 5) > p &
Q=$!
sleep 1
kill -HUP $P
sleep 1
ls .hg