(<inttypes.h>): Include if HAVE_INTTYPES_H.

(<inttypes.h>): Include if HAVE_INTTYPES_H.
("human.h"): Include.
(input_blocksize, output_blocksize, conversion_blocksize):
Now size_t instead of long.  0 means unset.
(skip_records, seek_record, max_records): Now uintmax_t, not long.
(w_partial, w_full, r_partial, r_full, r_truncate):
Now uintmax_t instead of unsigned.
(print_stats): Print counts as uintmax_t, not unsigned.
(main, skip): Check for overflow when computing file offsets.
(skip): Records count arg is uintmax_t, not long; blocksize arg is
size_t, not long.  Try lseek even on non regular files, as per comment.
(oc, col): Now size_t, not int.
(copy): No need to check max_records >= 0 any more, as the
default value is now effectively infinity.
Cast lseek arg to off_t.
(copy, copy_with_block): conversion_blocksize - col can never
be negative now, since it's unsigned, so rewrite loops to
avoid problems with unsigned.
(scanargs): Parse numeric args using uintmax_t, not int.
Check for overflow when converting block size args to size_t.
Blocksize options are now unsigned, and are now 0 when not set yet.
(parse_integer): Return uintmax_t, not int; accept new int * arg
to store error indicator, since all returned values are now valid.
Check for overflow when scanning integer.