docs: def ensure_dir(dir_path):
      """
      If DIR_PATH does not exist, makes it. Failing that, raises Exception.
      Returns True if dir already existed; False if it had to be made.
      """
      exists = dir_exists(dir_path)
      if not exists:
          try:
              os.makedirs(dir_path)
          except(Exception,RuntimeError), e:
              raise Exception("Unable to create directory %s. Cause %s" %
                              (dir_path, e))
      return exists