Added distribution option to RedisCluster in preperation for
implementation of commands which can be distributed by the client.
The two distribution modes will be:
* DIST_OOE : Maintain order of execution
* DIST_SPEED : Most efficient delivery
Either way, the RedisCluster object will need to return values that
were gathered in the same way they were sent in, but might execute
them in a different order if the option is set to DIST_SPEED.
