Make the translation procedure simpler

- Use langgen.php to both produce strings and freshen all po files.
- No need to run msgmerge manually.
- Enforce a single style of formatting for po files (-w1 --no-wrap)
  which makes it easier to diff.
Reformat existing translations.
Merge branch 'master' of https://github.com/wavexx/dl
Update fr_FR using new langgen.php to get cleaner patches next time