passed as TRUE.
Enclose hash_table_t::adaptive and buf_block_t::n_pointers in
#ifdef UNIV_DEBUG.
btr_search_drop_page_hash_index(): Enclose the corruption check
(which depends on buf_block_t::n_pointers) in #ifdef UNIV_DEBUG.
ut_is_2pow(): New function for testing if a number is zero or a power of two.
Use this function instead of bitwise arithmetics or ut_2_power_up() where
possible.