DATAREDIS-340 - Improve performance of zAdd elements when using jedis.

Optimize initial size of HashSet and use a Set implementation to check for score duplicates.
Move jedis version check outside loop.

Original PR: #101
CLA: 90520140903040912 (Konstantin Shchepanovskyi)
DATAREDIS-340 - Polish performance improvement of zAdd using jedis.

It turned out that the version check throttled performance so we moved things around to avoid iterating multiple times and still perform the check in a non intrusive way.