Closes connection, copies DB file, and opens again pointing to new file

        **Note** if filename equals current filename, does nothing!

def _do_save_as(self, filename):
        """Closes connection, copies DB file, and opens again pointing to new file

        **Note** if filename equals current filename, does nothing!
        """
        if filename != self.filename:
            self._ensure_filename()
            self._close_if_open()
            shutil.copyfile(self.filename, filename)
            self.__get_conn(filename=filename)