The stop-on-error option aims to solve the lack of damage_visitor support
in space_map::count_metadata and btree counting_visitor. To prevent
possibly silent errors during space map or btree counting, the option
stops the counting process immediately when a btree or bitmap error
was found.
The bitmap blocks are also validated to avoid potential false-alarm,
if broken bitmap is not counted, and the corresponding ref-count is
also zeroed.
