reserve binary statuses and commands for locking.

I will post a mail to memcached ML to describe details.

This patch reserves binary protocol statuses and commands used for server-side locking.

Server-side locking is implemented in [yrmcds][], a memcached-compatible KVS.
The location of the locking specification is here:
https://github.com/cybozu/yrmcds/blob/master/docs/locking.md

[yrmcds]: http://cybozu.github.io/yrmcds/