Fix bugs when computing length of large files.

Fix bugs when computing length of large files.
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.