rec_get_nth_field_offs_old(): Split from rec_get_nth_field_old().
rec_get_nth_field_old(): Reimplement as a constness-preserving macro.
dict_drop_index_tree(), dict_truncate_index_tree(): Note that rec is
an in/out parameter, as the B-tree root page number will be updated.
passed as TRUE.
Enclose hash_table_t::adaptive and buf_block_t::n_pointers in
#ifdef UNIV_DEBUG.
btr_search_drop_page_hash_index(): Enclose the corruption check
(which depends on buf_block_t::n_pointers) in #ifdef UNIV_DEBUG.
