* lib/human.c, lib/human.h (human_readable): Coalesce last two args

	* lib/human.c, lib/human.h (human_readable): Coalesce last two args
	into one, for convenience.  All callers changed.
	(human_block_size): New function.
	* lib/human.c: Include <config.h> only if HAVE_CONFIG_H.
	Include <stdlib.h> if HAVE_STDLIB_H;
	declare getenv unless HAVE_DECL_GETENV.
	(_): New macro.
	Include <argmatch.h>, <error.h>, <xstrtoul.h>.
	(DEFAULT_BLOCK_SIZE): New macro.
	(block_size_args, block_size_types): New constants.
	(humblock): New function.