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

(<inttypes.h>): Include if HAVE_INTTYPES_H.
("human.h"): Include.
(LONGEST_HUMAN_READABLE, enum Output_units): Remove.
(count_entry): Now returns uintmax_t, not long.
(human_readable_base): Renamed from opt_human_readable; value is now
zero or positive integer, not just zero or nonzero.
(output_units): Now an integer giving output size.
(tot_size): Now uintmax_t, not long.
(long_options, usage): Add --si or -H.
(main): Adjust to renamed option variables.
Use -H if BLOCKSIZE is SI.  Add -H.
(human_readable): Remove; rewritten and now in lib/human.c.
(print_size): Rewrite in terms of human_readable.
Accept extra arg to be printed after size; all callers changed.