this file path.  The child may or may not
        exist.

        @param name: the name of a child of this path. C{name} must be a direct
            child of this path and may not contain a path separator.
        @return: the child of this path with the given C{name}.
        @raise InsecurePath: if C{name} describes a file path that is not a
            direct child of this file path.
        Nr-