* tests/fold/fold-zero-width.sh: Check the shell was able to create
the redirection file, as intermittently on CentOS 5,6,7 this wasn't
the case, with the shell giving an xmalloc failure due to the ulimit.
Reported by William Bader and Bruno Haible.
* tests/fold/fold-characters.sh: Ensure we have independent verification
of the width of characters before testing based on those widths.
* tests/fold/fold-zero-width.sh: Likewise.
* tests/fold/fold.pl: Only compare the exit status,
as the error message can be translated.
* tests/fold/fold-zero-width.sh: Increase vm limit to avoid
failures on CentOS 5,6,7. Match the limit used in write-errors.sh
as per commit v9.5-255-g0bd149403
* src/fold.c (write_out): A new helper to check all writes.
(fold-file): Use write_out() for all writes.
* tests/fold/fold-zero-width.sh: Adjust to writing more
data in various patterns, rather than two buffers of NULs.
This is a more robust memory bound check, and the '\303' case
tests this particular logic change.
* NEWS: fold now exits immediately, not just promptly.
* src/fold.c (fold_file): Prefer putchar ('\n') to copying characters.
If we do not have room in the output buffer print it since it is not a
full line of text.
* tests/fold/fold-zero-width.sh: New test case.
* tests/local.mk (all_tests): Add it.
