French translation update

Hi Paul,

Here are some further changes to the French translation, respectively:
*   Translations for the latest messages
*   Some additional fixes and tweaks, including:
    -   `&` put back in menu labels
    -   A few remaining, sneaky typos corrected
    -   Various enhancements to existing translations

FYI, I asked for @Yonaba's feedback on those changes before pulling them back to you (he was totally OK with them :), as he made the original translation.

Regards,
Alexis (Fringale)