Add overflow and write error checks. Use uint_fast32_t, not
unsigned long, to do checksum calculation, as C99 says
uint_fast32_t should be no slower and might be faster.
Include <stdio.h> and "system.h" even if CRCTAB is defined,
so that the code will compile if CRCTAB is defined.
Include "human.h" if CRCTAB is not defined.
(uint_fast32_t): Define if it appears that stdint.h didn't.
(BIT, remainder, main, crctab): Use uint_fast32_t, not unsigned long,
for checksums.
(fill_r, remainder, main): Use ANSI prototypes.
(fill_r, remainder, main): Omit duplicate code.
(main): Use uintmax_t, not unsigned long, for file lengths.
Use size_t, not long, for result of fread.
Check for overflow when computing file lengths.
Check for write error immediately after printing a line, so that
we don't write to stdout indefinitely after an error.
that exists is a directory, don't treat it as if it were the only
argument. Before, `mkdir d; ls no-dir d 2>/dev/null' would act like
`ls d' and produce no output. Now, it prints `d:'.
code, since RLIMIT_RSS is similar (and is not standardized).
(default_sort_size): Don't allocate more than the RSS limit,
if this host has such a limit.
(usage, main): Add support for long options, and check option
syntax as POSIX requires, though (as usual for GNU apps)
options can follow file names unless POSIXLY_CORRECT is set.
Many diagnostic revamped.
(long_options): New constant.
(badfieldspec): New arg MSGID. Mark as noreturn.
(parse_field_count): New arg MSGID; if null, just return null on error.
(new_key): Renamed from key_init. All callers changed. Now allocates
the new key.
