Problem reported by Dennis Wydra in <http://lists.gnu.org/archive/html/bug-tar/2010-11/msg00082.html>. * scripts/backup.in: Accept "-l LEVEL". Be more systematic about backslashes inside ``; it shouldn't matter for modern shells but it might matter for older ones. * scripts/restore.in: Likewise. * scripts/backup.in: Adjust implementation of -t/--time to match the new implementation of -l/--level.