Replace page_t* or page_zip_des_t* parameters in some functions with
buf_block_t*.

buf_frame_get_page_zip(): Disable unless #ifdef UNIV_DEBUG || UNIV_ZIP_DEBUG.

btr_cur_t: Add buf_block_t* page_block.

btr_pcur_get_block(), btr_cur_get_block(), btr_cur_get_page_zip():
New functions.

btr_cur_position(): Add the parameter block.