Merge into Hibernate

[hgcummings]

The VersionCheckingFlushEntityEventListener can be used as is. However, this should arguably be the default behaviour. To make this happen it will be necessary to submit a pull request to hibernate-orm

Overall status

• Clone hibernate-orm
• Get tests running locally
• Apply change to DefaultFlushEntityEventListener
• Check for new test failures
• Work out what the correct behaviour should be in each failing case
• Fix test failures
• Submit pull request

Current task

There are three new test failures in hibernate-core. These are all to do with timestamp-based versioning (two cases result in NullPointerExceptions, and one throws a StaleObjectException due to a timestamp being set explicitly).