Use latest Jedis 2.4.2 & make integration test compatible to both Redis 2.6.x and 2.8.x

Hello!

grails-redis user requested to release backported version of Jedis.
(Currently latest Jedis is 2.4.2, and user requested v2.2.1 + back port to v2.2.2.)
See issue : https://github.com/xetorthio/jedis/issues/589

I'm not grails user, but I did give it a try.
I changed Jedis version and fix some unit tests.
(it's not related to Jedis, it's related to Redis version - ttl result is different with Redis 2.6 and 2.8. see http://redis.io/commands/ttl)

It seems that latest Jedis works flawlessly in point of view as grails-redis tests.
(I'm using "grails test-app") 
So I request to merge this change.

Please review and comment!