Logging of the size of different message types.

* Maximum detected size per message type is logged once
* Default configuration disables this feature
Changed design of RemoteWatcher due to cleanup race, see #3265

* The problem was a race caused by HeartbeatReq sent out, and
  the watchee terminated immediately. That caused the RemoteWatcher
  peers watching each other without any other watch registered.
  It is racy.
* Instead of one-way heartbeats from the side beeing watched I
  changed to ping-pong style. That makes the problem go away
  and simplifies a lot of things in RemoteWatcher.
Merge pull request #1385 from akka/wip-3280-log-payload-size-patriknw

Logging of the size of different message types.
Wait on shutdown of extra actor systems in tests. See #3217
Merge pull request #1395 from akka/wip-3217-remotedeathwatchspec-failure-ban

Wait on shutdown of extra actor systems in tests. #3217
Actor fields are cleared after Terminated is sent. See #3311
Fixed decoding in the case of fragmented delimiters #3306

 - also improved tests
Merge pull request #1403 from drewhk/wip-3306-fragmented-delimiter-drewhk

Fixed decoding in the case of fragmented delimiters #3306
TypedProps now uses deploy information #3315
Merge pull request #1405 from drewhk/wip-3315-typedprops-deploy-drewhk

TypedProps now uses deploy information #3315
Merge pull request #1404 from akka/wip-3311-localactorrefproviderspec-failure-ban

Actor fields are cleared after Terminated is sent #3311
Merge pull request #1401 from akka/wip-3265-heartbeating-race2-patriknw

Changed design of RemoteWatcher due to cleanup race, see #3265
Fixed race causing missed wakeups
fix TestTimeSpec, see #3317
Removed unnecessary comment
Merge pull request #1408 from drewhk/wip-selector-wakeup-miss-drewhk

Fixed race causing missed wakeups
Merge pull request #1409 from akka/wip-3317-awaitAssert-∂π

fix TestTimeSpec, see #3317
io-tests: simplify TcpConnectionSpec in preparation for coming modifications

This doesn't change any test logic, it merely structures the test fixture code a bit differently to make it easier to insert additional mocks required for coming additions.
io: small clean-ups
io: remove SelectionKey lookup and reduce IO-layer-internal message volume