Catch up CHANGES.txt for recent deprecation removals.
Clean up some warnings.
Remove deprecated WebServer#addExecutionLimitFilter(int, Guard).
Consistency checker: verify that nodes in the node store are in the label scan store.
Use tx diff to reclaim unused records.

Instead of recording dynamic records for labels as deleted in the
transaction log, use the fact that we store both the state before the
transaction and the state after, to only require storing the used ones.
The set of unused records can be computed as the difference between the
set of records used before and the set of records used after.

In effect reverts (most of) 069edcfe7dcbb07f43599c91ec76c154f49b1934.
Merge pull request #1445 from benbc/2.0-deprecation-CHANGES.txt

Catch up CHANGES.txt for recent deprecation removals.
Merge pull request #1451 from boggle/2.0-index-update-using-before-image

Ensure that we remove index entries when labels and properties of a node...
Merge pull request #1450 from thobe/2.0-delete-by-delta

Use tx diff to reclaim unused records.
Remove QuickReadPerformanceTest.

This class was most likely added to org.neo4j.graphdb by mistake.
Merge pull request #1452 from jakewins/2.0-remove-deprecated-stuff

2.0 remove deprecated stuff
Merge pull request #1453 from apcj/2.0-ccheck-node-to-label-scan

Consistency checker: verify that nodes in the node store are in the label scan store.
Merge pull request #1454 from chrisvest/remove-quick-read-performance-test

Remove QuickReadPerformanceTest.
Add merge functionality to core API

This contains work from TL, CV, BBC.

Details:

o Core API
  o Add new Merger and MergeResult interfaces to core API
  o Add GDS#getOrCreate(label1, label2, ...).withProperty(k, v).merge()
  o Add UniqueFactory#asMerger()
  o Update javaocs and documentation examples for creating unique nodes

o Change locking of nodeGetUniqueFromIndexLookup
  o New contract: RLock held afterwards if node was found, WLock otherwise
  o Introduce ReleasableLock as a means of either manually releasing locks or registering them with the transaction

o Loosely related fixes
  o Fix InMemLabelScanStore to handle queries for labels that haven't been used before
  o Fix InMemoryIndex to not apply updates idempotently in online mode
  o Make KernelTransaction.assertOpen() public
  o Make Statement.assertOpen() public
  o Make NotInTxException extend IllegalStateException instead of being a plain RuntimeException