This commit implements UNLINK for Redis, RedisCluster, and RedisArray.
To a client library UNLINK behaves identically to DEL so we can use the
same handlers for both.
* Added a test specifically for RedisCluster to test slave failover
settings.
* Added an option to specifically disable colorization, as well as
a mechanism to determine if the output is being piped, such that
we can turn colorization off in that case as well.
This commit reworks the unit tests such that all three classes
(Redis, RedisArray, and RedisCluster) can be tested using the
TestRedis.php script.
Now, when running TestRedis.php an option can be passed for which
part of phpredis we would like to test (defaults to Redis).
