Essence 0.68 improve network bandwidth and JCache support.

Changes
- Cluster store meta data extends CacheEntry<K,V> extends Map.Entry<K,V>
This changed the data format and how snap shots and bootstraps are sent.

- Made Datable binary format safer. Support given for objects which write more or less data or have incompatible versions of data.

- Correct @ThreadSafe doco and Immutable(false) supported.

- Improved CacheEntry statistics support for all fields except getCost(). LastAccessTime must be enabled to be recorded.

- Data file now include a format description to support future format changes.

- Performance tuned for Linux.

- Increased unit and performance test coverage.

- File in clusters and collections added to ${java.io.tmpdir} are set to deleteOnExit to improve repeatability of tests.

- Added a test ant target.