adaptive hash index for a B-tree page. (Bug #16582)
btr_search_drop_page_hash_index(): Retry the operation if a hash index
with different parameters was built meanwhile. Add diagnostics for the
case that hash node pointers to the page remain. This fix is from Heikki.
btr_search_info_update_hash(), btr_search_info_update_slow():
Document the parameter "info" as in/out.
Note that buf_block_t::index should be protected by btr_search_latch
or an s-latch or x-latch on the index page.
btr_search_drop_page_hash_index(): Read block->index while holding
btr_search_latch and use the cached value in the loop. Remove some
redundant assertions.
