(total_blocks_deleted): New variable

(total_blocks_deleted): New variable
(set_start_time): Set volume_start_time and last_stat_time as well
(set_volume_start_time): New function
(compute_duration): Do not call set_start_time, update
last_stat_time instead. Use it in calculation instead of
start_time, which is now set only once, upon startup.
(print_total_written): Removed.
(print_total_stats): New function for printing byte/speed statistics.
(_open_archive): Detect attempts to update compressed archives.
(_gnu_flush_write): Always update prev_written.
(open_archive): Call set_volume_start_time.