(record_start_block, save_totsize, save_sizeleft, real_s_totsize,

real_s_sizeleft, current_block_ordinal): Now off_t.
(write_error): Arg is now ssize_t.
(child_pid): Now pid_t.
(available_space_after): Now size_t.

(child_open_for_compress, child_open_for_uncompress, flush_write,
open_archive, flush_write, write_error, flush_read, close_archive):
Use pid_t, ssize_t, size_t when appropriate.  Remove now-useless
casts.  Use unsigned long to print *_t types, except use
STRINGIFY_BIGINT for off_t.