def movePluginsUp(plugin_type, ids_to_move):
    """ Move a set of plugins "up" in their list.

        o 'plugin_type' must be one of the known types, else raise KeyError.

        o 'ids_to_move' must be a sequence of ids of current plugins
          for that type.

          - If any item is not the ID of a current plugin, raise ValueError.
        """
