Add multi sentinel support
SentinelMonitored improvement: query all sentinels for master address, instead of just the first one
Sentinels auto discovery: we maintain a hashmap of sentinel clients and update it when sentinel processes go up and down, by subcribing to '+sentinel' and '+sdown'
1. Earlier reconnect on master failover 2.Handle address change during the write phase as well
Use sentinelClients.synchronized instead
Merge branch 'mt/multi_sentinel' of git://github.com/tovbinm/rediscala into tovbinm-mt/multi_sentinel

Conflicts:
	src/main/scala/redis/Redis.scala
	src/main/scala/redis/actors/RedisClientActor.scala