addDirectory( $directoryName [, $fileName ] )
        Append a member created from the given directory name. The directory
        name does not have to name an existing directory. If the named
        directory exists, the file modification time and permissions are set
        from the existing directory, otherwise they are set to now and
        permissive default permissions. $directoryName must be in local file
        system format. The optional second argument sets the name of the
        archive member (which defaults to $directoryName). If given, it must
        be in Zip (Unix) format. Returns the new member.