mailmap: Adds Christophe Courtaut

Signed-off-by: Christophe Courtaut <christophe.courtaut@gmail.com>
Merge pull request #1055 from kri5/master

mailmap: Adds Christophe Courtaut

    git shortlog -nes 

shows only one Christophe Courtaut proof that the .mailmap addition is working.

Reviewed-by: Loic Dachary <loic@dachary.org>