Change the current working directory and update all the paths in the
        workspace.  This is useful for commands that have to be run from a
        certain directory.

def cd(self, *subpaths):
        """
        Change the current working directory and update all the paths in the
        workspace.  This is useful for commands that have to be run from a
        certain directory.
        """
        target = os.path.join(*subpaths)
        os.chdir(target)