btr_search_build_page_hash_index(), fsp_parse_init_file_page(),
ibuf_parse_bitmap_init(): Replace page_t* with buf_block_t*.

buf_read_ibuf_merge_pages(): Add const qualifiers.  Retrieve zip_size.

ibuf_merge_or_delete_for_page(): Replace page_t* with buf_block_t*.
Add parameter zip_size.