determined from flag == BTR_CUR_ABORTED. This flag value was previously
never tested for. It was only assigned to, in the only place where
leaf_in_buf_pool would be set FALSE.
btr_cur_search_to_nth_level(): Do not initialize cursor->leaf_in_buf_pool.
btr_pcur_was_buffered(): Remove. The only caller, row_search_index_entry(),
will switch (cursor->flag) and handle BTR_CUR_ABORTED as well.
row_purge_remove_sec_if_poss_low(): Remove the assertions on leaf_in_buf_pool.
btr_cur_t: Move page_block to page_cur_t::block.
page_cur_get_block(), page_cur_get_page_zip(): New functions.
page_cur_position(): Add parameter block.
Remove many page_zip parameters, now that there is page_cur_get_page_zip().
Replace some page, page_zip parameters with block.
Add some const qualifiers to function parameters and remove casts.
PAGE_HEAP_NO_INFIMUM, PAGE_HEAP_NO_SUPREMUM, PAGE_HEAP_NO_USER_LOW:
New constants.
Replace some cursor code in low-level diagnostic functions with
direct management of rec, because buf_block_t::buf_fix_count may be 0
when the functions are called, and debug assertions would fail.
