Update AbstractNodeQueue.java

Avoid spinning on head when a peek/poll observes a null next but the queue is not empty.
Update AbstractNodeQueue.java

language language....
Fix isEmpty() and count()

isEmpty() need not rely on peek(which is intended for consumer use) and instead compare head to tail.
count() should stop counting at max int to avoid wrap.
Fixe documentation to state consumer only access is allowed to poll/peek/peekNode/pollNode
Doc stars err
Forgotten bracket
=per #15590 Increase efforts to in-order on start of ALOD

AtLeastOnceDelivery can delivery out-of-order, and that's OK.
Although, in the case of message replay followed by taking user land
commands which may trigger `deliver` calls, it is nicer to at least once
try to send the replayed but not confirmed deliveries *first*, before
sending the completely new deliveries.

This change acomplishes this by triggering redelivery explicitly when
recovery has finished, and setting the timestamps on these messages a
bit in the past, so they hit their redelivery deadline right away during
this recovery induced redelivery.

Resolves #15590
Merge pull request #15653 from akka/port-impr-efforts-to-in-order-during-replay-ALOD-ktoso

=per #15590 Increase efforts to in-order on start of ALOD (for Validation)
=doc #15638 clarify message ordering rule

add a missing reference to the fact that it only applies to messages sent directly
=15648 ker Use wildcard in microkernel classpath

* scala-library.jar had changed name to scala-library-2.10.4.jar
* use wildcard to avoid same problem when scala-library version is changed
* the wilcard will only include jar files in the lib directory, and not the
  lib/akka directory, see 'Understanding class path wildcards'
  http://docs.oracle.com/javase/6/docs/technotes/tools/windows/classpath.html

(cherry picked from commit 996de05b44531bda517ef8ee274a34ad76e9716f)
Merge pull request #15660 from akka/wip-15648-classpath-master-patriknw

=15648 ker Use wildcard in microkernel classpath (for validation)
Improve docs for AtLeastOnceDelivery recovery

The Eventsourced migration guide currently suggested AtLeastOnceDelivery is
less useful than it actually is :)
Merge pull request #15662 from raboof/AtLeastOnceDeliveryDocs

Improve docs for AtLeastOnceDelivery recovery
Merge pull request #15596 from nitsanw/master

Update AbstractNodeQueue.java to avoid redundant reads of head in peekNode
!con #15496 Remember entries in cluster sharding

- Move all entry related logic out of the ShardRegion and into a
  new dedicated child `Shard` actor.
- Shard actor persists entry started and passivated messages.
- Non passivated entries get restarted on termination.
- Shard Coordinator restarts shards on other regions upon region failure or handoff
- Ensures shard rebalance restarts shards.
- Shard buffers messages after an EntryStarted is received until state persisted
- Shard buffers messages (still) after a Passivate is received until state persisted
- Shard will retry persisting state until success
- Shard will restart entries automatically (after a backoff) if not passivated and remembering entries
- Added Entry path change to the migration docs