copy postgresql.conf to postgresql.conf.backup to be able to retrive configuration files
            - originally stored as symlinks, those are normally skipped by pg_basebackup
            - in case of WAL-E basebackup (see http://comments.gmane.org/gmane.comp.db.postgresql.wal-e/239)

def save_configuration_files(self):
        """
            copy postgresql.conf to postgresql.conf.backup to be able to retrive configuration files
            - originally stored as symlinks, those are normally skipped by pg_basebackup
            - in case of WAL-E basebackup (see http://comments.gmane.org/gmane.comp.db.postgresql.wal-e/239)
        """
        try:
            for f in self._configuration_to_save:
                config_file = os.path.join(self._config_dir, f)
                backup_file = os.path.join(self._data_dir, f + '.backup')
                if os.path.isfile(config_file):
                    shutil.copy(config_file, backup_file)
        except IOError:
            logger.exception('unable to create backup copies of configuration files')
        return True