Return a list of the filenames specified in the ``results`` argument, which
    are not present in the dest_dir.

def _get_missing_results(results, dest_dir):
    '''
    Return a list of the filenames specified in the ``results`` argument, which
    are not present in the dest_dir.
    '''
    try:
        present = set(os.listdir(dest_dir))
    except OSError as exc:
        if exc.errno == errno.ENOENT:
            log.debug('pkgbuild.built: dest_dir \'%s\' does not exist', dest_dir)
        elif exc.errno == errno.EACCES:
            log.error('pkgbuilt.built: cannot access dest_dir \'%s\'', dest_dir)
        present = set()
    return sorted(set(results).difference(present))