assoc: add mh_i64
assoc: add mh_i64

Need it for looking up vinyl indexes, ranges, and runs during recovery
(will be used later).

mejedi/tarantool,rtsisyk/tarantool,rtsisyk/tarantool,rtsisyk/tarantool,mejedi/tarantool,rtsisyk/tarantool,mejedi/tarantool,mejedi/tarantool