+per #3746 Remote sharing of LevelDB for testing purposes

Further changes

- remove obsolete identity checks in Eventsourced
- fix wrong serialize-messages config in tests

akka-persistence/src/main/scala/akka/persistence/JournalProtocol.scala

@@ -9,6 +9,8 @@ import scala.collection.immutable
 import akka.actor._
 
 /**
+ * INTERNAL API.
+ *
  * Defines messages exchanged between processors, channels and a journal.
  */
 private[persistence] object JournalProtocol {