I18n: Update translation fr (100%).

164 translated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
Add <Ctrl><Alt>l shortcut for screen locking (xflock4) (bug #10728)
Don't drop startup notify hint when resetting to defaults (bug #10630)
Avoid double forking when spawning external apps (bug #9373)

Some security conscious applications such as pkexec detect double forks
and refuse to operate. Avoiding the double fork here is very simple.

See https://bugzilla.xfce.org/show_bug.cgi?id=9373
and https://bugzilla.gnome.org/show_bug.cgi?id=686059