[sane-devel] translations: update french translation

[Yann E. MORIN]

This patch updates the french translation. Of notable interest:
- all 897 messages are translated
- no fuzzy messsage remains

I have not reviewed all messages, just those that were not translated,
and those that were fuzzy. I did spot a few errors that I fixed. Also,
in French, the correct translation for 'scanner' is 'numériseur', but
is not widely used, and we do use 'scanner'. I have changed two
occurences of 'numériseur' back to 'scanner'.