!per #3761 Reliable channels

- Built-in redelivery mechanism for Channel and PersistentChannel
- redelivery counter on ConfirmablePersistent
- redeliveries out of initial message delivery order
- relative order of redelivered messages is preserved
- configurable redelivery policy (ChannelSettings)
- Major refactorings of channels (and channel tests)
- Throughput load test for PersistentChannel

Todo:

- Paged/throtlled replay (another pull request)
- Resequencer (another pull request)

akka-docs/rst/scala/code/docs/persistence/PersistencePluginDocSpec.scala

@@ -32,6 +32,9 @@ object PersistencePluginDocSpec {
       //#snapshot-config
       akka.persistence.snapshot-store.local.dir = "target/snapshots"
       //#snapshot-config
+      //#native-config
+      akka.persistence.journal.leveldb.native = off
+      //#native-config
     """
 }
 
@@ -80,6 +83,9 @@ object SharedLeveldbPluginDocSpec {
       //#shared-journal-config
       akka.persistence.journal.plugin = "akka.persistence.journal.leveldb-shared"
       //#shared-journal-config
+      //#shared-store-native-config
+      akka.persistence.journal.leveldb-shared.store.native = off
+      //#shared-store-native-config
       //#shared-store-config
       akka.persistence.journal.leveldb-shared.store.dir = "target/shared"
       //#shared-store-config