Made extent_zone_t::offset_to_id be const.
Made extent_zone_t use a priority queue to manage free extents instead of a disturbing sort of linked list.
Made extent_zone_t::extents be a vector.
Made extent_index return an unsigned int, not an int.
Made mark_live use unsigned int, not int, for extent_id.
Made reconstruct_free_list just iterate using extent ids instead of offsets.