fix some typos (main.cpp to be synced after release, because of string freeze)

[kdenlive] / AUTHORS

Jean-Baptiste Mardelle <jb@kdenlive.org>: main developer and maintainer
Marco Gittler <g.marco@freenet.de>: MLT effects, timeline, audio thumbs
Jean-Michel Poure <jm@poure.com>: rendering profiles customisation
Ray Lehtiniemi <rayl@mail.com>: bug fixing, etc.
Dan Dennedy <dan@dennedy.org>: bug fixing, etc.
Jason Wood <jasonwood@blueyonder.co.uk>: original KDE 3 version author (not active anymore)