tests/test-issue433

enhance Makefile for language translators

To update a po-file just do 'make i18n/xx.po'. No other po-file will
be touched.

#!/bin/sh
# http://www.selenic.com/mercurial/bts/issue433

hg init a
cd a
echo a > a
hg commit -Ama

hg parents -r 0 doesnotexist
true