Thin 3.0: Improve getAll and putAll partition awareness

Currently, getAll and putAll use the first key for partition awareness.

This causes extra network hops when other keys in the list belong to different nodes.

• Client should split the data set into per-node sets and send multiple requests in parallel. This should improve performance significantly for large sets.
• To ensure atomicity, use client observable timestamp. Talk to ascherbakov for more details.