Log at WARN level in case of contradicting PersistenceUnitManager setup

[odrotbohm]

If users configure a LocalContainerEntityManagerFactoryBean and accidentally set both a persistence unit name and packages to scan, the latter are ignored but the message pointing to the invalidity of this setup is only logged at debug level. The observable misbehavior is that apparently the entity scanning silently does not work.

Here's an example StackOverflow question.