Fix a memory corruption bug: in 32-bit computers, every 4 billionth malloc outside innodb_additional_mem_pool_size was mistreated when freeing the memory; this could corrupt the InnoDB additional mem pool and could have caused crashes anywhere, also inside MySQL, or even database corruption! the bug exists also in 3.23 and 4.1; workaround: configure innodb_additional_mem_pool_size big enough