Update redis to 2.8.9.

--[ Redis 2.8.9 ] Release date: 22 Apr 2014

# UPGRADE URGENCY: LOW, only new features introduced, no bugs fixed.

* [NEW] The HyperLogLog data structure. You can read more about it
        in this blog post. http://antirez.com/news/75
* [NEW] The Sorted Set data type has now support for lexicographic range
        queries, check the new commands ZRANGEBYLEX, ZLEXCOUNT and
        ZREMRANGEBYLEX, which are documented at http://redis.io.

--[ Redis 2.8.8 ] Release date: 25 Mar 2014

# UPGRADE URGENCY: HIGH for Redis, LOW for Sentinel. There is a potentially
                   critical bug fix causing data loss in Redis but it requires
                   a combination of disk full and the use of the
                   SHUTDOWN command.

* [FIX] Fixed data loss when SHUTDOWN was used with a disk full condition.
* [FIX] Fixed a memory leak in the SORT syntax error processing.
* [FIX] When Sentinel down-after-milliseconds parameter is modified at runtime
        now it gets propagated to all the slaves and sentinel instances
        of the master.
* [FIX] `install_server.sh` script finally fixed.
* [FIX] Different fixes to maxclients handling.

* [NEW] Sentinels are now able to send update messages in a peer-to-peer
        fashion even if no Redis instances are available. Now the Sentinel
        liveness property that the most updated configuration in a given
        partition is propagated to all the Sentinels is extended to partitions
        without reachable instances.
* [NEW] Sentinel safety properties are now ensured in a crash-recovery system
        model since some state is persisted on disk before replying to other
        nodes, and reloaded at startup.
* [NEW] Sentinel now uses CLIENT SETNAME so that it is easy to identify
        Sentinels using CLIENT LIST among other clients.
* [NEW] Sentinel failure detection and reconnection code improved.
* [NEW] Use all 24 bits (instead of 22) for the Redis objects LRU field.
        Note that the new LRU algorithm using eviction pools was not backported
        from unstable for safery / code maturity concerns.
* [NEW] Majory speedup for the INFO command (it is now 6 times faster).
* [NEW] More Sentinel unit tests.
* [NEW] New command DEBUG ERROR returns the specified error. Example:
        DEBUG ERROR "LOADING database". This is handy to write Redis client
        libraries unit tests.
* [NEW] redis-cli now supports multi-line editing via updated linenoise lib.


(fhajny)