fixes #3138 . Update istatistics after operation is run and  before resp...

...onse is send to client
Maybe it works for now, but ```PartitionClientRequest``` is abstract and you are also deciding on behalf of the future implementors of this class by calling ```afterProcess()``` before actual process so it is not fair for the future implementors even it works for current get/put/remove implementations. It seems to me a possible violation of Polymorphic open/closed principle here (http://en.wikipedia.org/wiki/Open/closed_principle).