uu_avl_nearest_next
data = uu_avl_nearest_next(mod_index_avl, idx);
data = uu_avl_nearest_next(problem_uuid_avl, idx);
data = uu_avl_nearest_next(rsrc_index_avl, idx);
void *uu_avl_nearest_next(uu_avl_t *, uu_avl_index_t);