Omits norms and document frquency statistics from lucene documents

They are not used a.t.m. and removing them reduces disk space to 50%
from basic measurements.
Also the previous code added to node id fields ("id" and "_id_"),
which was also removed here.
Cheaper StatementState ref counting

o Cheaper ref counting
ReferenceCountingStatementOperations adds sharing of StatementState instances
among potentially multiple consumers, where they will be individually
closed, but the statement state not actually closed until ref count
reaches 0.

Previously a new "referenced" StatementState was returned for each of
these shared instances. And the single reason for that was to prevent and
fast-fail closing any given statement state instance multiple times. There
were no other such checks, just for closing. Keeping in mind that
KernelAPI is an internal API, having such checks should merely exist for
debugging purposes, _when_ debugging; not at runtime in production. As
seen by performance benchmarks all these StatementState instances are
costly.

This commit returns the same "referenced" StatementState (just inc/dec its
ref counter) for all the same shared instances to gain performance.

o StatementStateOwners moved to ThreadToStatementContextBridge since this
functionality is specific to the core API, and ThreadToStatementContextBridge
is specific to the core API.
Add tests that clarify the semantics of DiffSets.apply

o DiffSets.apply now filters out added elements from source, too
Removed redundant relationship striped locking

When striped locking functionality moved into a new class LockStripedCache
the logic for loading relationships wasn't change even if the cache got
extended with locking. So there was double locking of every loaded
relationship. This just completes that change by removing some code from
getRelationshipForProxy that moved into LockStripedCache.
Merge pull request #967 from tinwelint/2.0-cheaper-refcounting

Cheaper StatementState ref counting
Merge pull request #909 from tinwelint/2.0-lucene-stripped

Omits norms and document frquency statistics from lucene documents
Added CreateUniqueAst to handle creation of CreateUniqueStartItems
Adds CREATE UNIQUE to the experimental parser