Remove cyclic dependency of water and hex.
Bug fix: Invalidate the NA count after writing to a NewChunk with set_impl
Fix the Vec.set(long, val) API to actually set the value in the K-V store by calling close() every time set() is called.  Otherwise, only the pojo is modified on the writing node.

For a faster (still slow) path, use the Vec.Writer API as follows:
Vec.Writer vw = vec.open();
vw.set(i,val1);
vw.set(j,val2);
vw.close();

Note: This still doesn't fix the case where writes happen in parallel.
Merge branch 'master' of https://github.com/0xdata/h2o
Update NewVectorTest to use vec.set() instead of chunk.set() and chunk.close().
Fix comment.
Add postWrite() to Vec.Writer.close()
Add Vec.preWriting() to Vec.Writer.open() call.
Use Futures in Vec.close()
Merge branch 'master' of https://github.com/0xdata/h2o
Fix Vec.set() "slow/blocking/closing" API:
1) Invalidate cache after setting a value, otherwise the next read is wrong.
2) Use Futures since default-behavior (passing null as fs) didn't block.
Update/Fix NewVectorTest:
1) Test distributed write/reads, not just single-node.
2) use Futures to make close() blocking.
3) Add test of faster API: Vec.Writer
Merge branch 'master' of https://github.com/0xdata/h2o