fix flaky test: t/binary-extstore.t
fix flaky test: t/binary-extstore.t

Had a bunch of sleep 4's in there. Guess that was before I switched to
wait_for_ext()... put in a version of that for the binary protocol
since the client is slightly different.

dormando/memcached,memcached/memcached,memcached/memcached,memcached/memcached,dormando/memcached,dormando/memcached,dormando/memcached,memcached/memcached,memcached/memcached,dormando/memcached