@Inject EntityManager outside @Transactional creates stale connections

[stackoverflow](http://stackoverflow.com) handles this issue in a three year old post, but the implementation is still the same;

[ Lifecycle management of EntityManager is kind of broken if it's injected via @Inject EntityManager](http://stackoverflow.com/questions/18101488/does-guice-persist-provide-transaction-scoped-or-application-managed-entitymanag). Check answer 7 and 16.

There should be a safety check for transaction-scoped semantics which prevents EntityManager instances outside @Transactional methods.