hash index, because it might occupy the chunk we would like to free.
TODO: In btr_search_check_free_space_in_heap(), release the block if
btr_search_latch is not immediately available.
buf_pool_shrink(): Split from buf_pool_resize().
btr_search_disabled: New variable, similar to srv_use_adaptive_hash_indexes
that was removed earlier.
btr_search_disable(): New function: disable and purge the adaptive hash index.
btr_search_enable(): New function: enable the adaptive hash index.
ha_clear(): New function: Empty a hash table and free the memory heaps.
Replace buf_frame_t* guess with buf_block_t* guess in order to avoid
a buf_block_align() call.
trx_undo_t: Replace page_t* guess_page with buf_block_t* guess_block.
btr_search_t: Replace page_t* root_guess with buf_block_t* root_guess.
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.
