Test to reproduce wrong account balance after upgrade from 2.12 to 2.13

After upgrading from 2.12 to 2.13 I noticed that some account balances changed.
I debugged into the sources and managed to create a minimal example to reproduce the problem (this pull request).
I have a Transaction that contains two identical TransactionEntry (have the same hash). When the XML-File is loaded, only one remains in the Transaction.Set<TransactionEntry> transactionEntries. When the file is stored, the TransactionEntry is lost for good.

With jgnash 2.12 this worked fine. TransactionEntries where stored within a List instead of a HashSet

I think the problem was introduced with
596a9b8ce2e8c5a91233d186ff2481067a17c044 Using a set significantly improves Hibernate update performance.

To reproduce the problem merge to master, adjust the EngineFactory call and run the test.