Cocoa: avoid displaying window when command-line contains '-h' or '-help'

There was already a check in place to avoid displaying a window
in certain modes such as vnc, nographic or curses.

Add a check for '-h' and '-help' to avoid displaying a window for a split-
second before showing the usage information.

Signed-off-by: Alexandre Raymond <cerbere@gmail.com>
Signed-off-by: Andreas Färber <andreas.faerber@web.de>
