Fix French translation.

* Translation of "notify" has been changed to the literal translation
  "notifier" which seems more appropriate (cf. recent thread on
  AUR-general)

* Uniformization of the translation of "flag"

* Addition of "TU" besides the translation of Trusted User as user may
  not understand that Trusted User and "Utilisateur de confiance" are
  the same thing

* Some capitalization correction (in French you don't put capital
  letters in the middle of a sentence as you do eg for title in
  English).

* "unsupported" translation has been replaced by "unsupported" (with
  quotes) as it makes no sense to translate it

* "Safe" translation has been replaced by "sûr" has it seems more
  appropriate than "sain" (sane)

Lukas: Added translator to "AUTHORS".

Signed-off-by: Lukas Fleischer <archlinux@cryptocrack.de>