Consequent French translation update

As discussed on the aborted pull request #360, I split the update into two commits:
- one resulting from a push+pull of the Bertram25:master French translation to Transifex, so that we let Tx wreak havoc in the diff because it does not want to crop lines after ~80 characters;
- one to actually apply the translation update from Transifex.

Note that Transifex reinitialise the file's descriptive header to:
> # SOME DESCRIPTIVE TITLE.
# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
# This file is distributed under the same license as the PACKAGE package.

I edited it manually to restore it to something meaningful, but this would have to be done each time sadly, that's one of Transifex's long standing issues.