FIX: Rethrow error in commit path of callbacks

[rPraml]

Actual behaviour
If you have callbacks in your transaction and they fail due any reason, the error is just added to the log and subsequent callbacks will be invoked and finally the transaction will be commited

Expected behaviour
If a callback in the commit path (preCommit/postCommit) has a problem, the exception should be thrown up to the caller and the transaction should NOT be committed, if a preCommit hook fails.

In our situation, we performed a DB.save on an entity. The preCommit hook on that entity performed some DB access in an nested transaction. The JDBC driver failed with an error and the nested transaction perfomed a roll-back. As there were no save-points involved, the whole transaction is rolled back. For the caller the DB.save seems to be successful. We discovered the error, when we reviewed the logs and see that there was a problem.

Our suggestion is, that exceptions, that happen in a "preCommit" or "postCommit" hook should always be rethrown up to the caller.
For "preRollback" and "postRollback" we are a bit unsure, and we keep the behaviour as it is (log exception and continue)