Atomic increment/add

This is a new pull request for @KevinOrtman atomic increment feature (https://github.com/tsuna/opentsdb/pull/2) that was made against 1.X code base and never added master.

Basically the same code, except minor changes for 2.0 code base and using add-keyword instead of inc. There was some discussion about this in above mentioned pull request.

Another thing done is that I have disabled scheduleForCompaction(...) within the increment. Does this mean that a row created by add will never be compacted?
I would guess that compaction and atomic increment for already compacted values is not good fit.

Would like to see a discussion if this could be incorporated into the project.