'Create a restore checkpoint with the name specified as ``msg``'

def add_savepoint(self, msg):

    self.commit_all_editors_to_container()
    nc = clone_container(current_container(), self.mkdtemp())
    self.global_undo.add_savepoint(nc, msg)
    set_current_container(nc)
    self.update_global_history_actions()
