This was imported into libcperciva on 2023-08-16, so the code in spiped
should follow suit.

This should have been part of:
    2019-10-15 tests/nc-server: add bit-limited echo server
    ee4d29e

We didn't notice earlier, because a pair of errors cancelled each other out:

1) there was no "success, return 0" in write_bps(), so it always
   returned a -1.

2) callback_read() did not check the returned value from the callback
   function, so that -1 was ignored.

Reported by:	cppcheck-2.11

I added sanity checks in:

    2022-08-23 perfests/{recv,send}-zeros: add sanity checks
    c87a40b

which were a bit confused (i.e. checking that a (size_t) was not <= 0).
At that time:

- buflen in recv-zeros/main.c was a (ssize_t), whereas
- buflen in send-zeros/main.c was a (size_t), and
- clang-tidy 14 and lower could not follow our PARSENUM().
  macro to understand that:

    if (PARSENUM(&buflen, argv[2], 1, SSIZE_MAX))
            goto err0;

  would always result in a positive, non-zero value in buflen.

This commit:

- makes both files use (size_t)buflen.
- adds bounds to PARSENUM(&count...
- eliminates the post-PARSENUM sanity checks.

  That last point will make clang-tidy versions below 15.0.0 (2022-09-6)
  complain about the code, but inspection shows that it's correct.
  And it's normal for clang-tidy to have tons of complaints anyway;
  I normally disable ~60 types of warnings.

- also, this commit cleans up the #includes.

    The XSI extensions specifying the -a and -o binary primaries...
    have been marked obsolescent... Scripts using these expressions
    should be converted to the forms given below...
        test "$1" -a "$2"
    should be written as:
        test "$1" && test "$2"
    https://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html

https://www.shellcheck.net/wiki/SC2166

Reported by: shellcheck-0.9