crc32() hashing for user_email_hash

The 3.0.6 version use the crc32() function for hashing user email. This get the problem with password remind when phpbb move from 32 bit to 64 bit systems, because the php crc32() function return different values in 32 and 64 bit systems. For example, the phpbb_email_hash() for email 'dudarik@yandex.ru' for 32 bit systems return -80635440617 and 348861289017 for 64 bit systems.