* tests/extrac17.at: Add --warning=no-timestamp, to avoid
bogus warning due to NFS clock skew.
* tests/remfiles01.at: Discard diagnostics that some shells
generate about broken pipes.
* tests/sigpipe.at: Likewise.
* tests/remfiles01.at: Fix typo: "test $EC" was written where
"test $EC -ne 0" was intended.