Fix race in CircuitBreakerMTSpec.openBreaker, see #2953

* The problem was that the breaker is asynchronous so it may
  take some extra time to open.
* Was able to reproduce with a sleep in onComplete in
  CircuitBreaker L303
* Added an extra awaitCond in case the normal (quick)
  failing calls don't open the breaker
Making sure that the current Threads' UEH is called when using Akka FJP in Dispatcher as ExecutionContext
Dead letters containing remote envelopes handled correctly #2959

 - New DeadLetter class for handling remoting specific envelopes
 - Fixed error handling of name lookups
 - Name lookup is now handled via futures (future refactor opportunity)
Merge branch 'master' into wip-2974-escalate-uncaught-exceptions-√
Merge pull request #1077 from drewhk/wip-2959-cluster-deathwatch-fix-drewhk

Dead letters containing remote envelopes handled correctly #2959
Merge pull request #1085 from akka/wip-2974-escalate-uncaught-exceptions-√

Making sure that the current Threads' UEH is called when using Akka FJP ...
ignore automatically assembled files in akka-osgi resources dir
Merge pull request #1082 from akka/wip-2953-openBreaker-patriknw

Fix race in CircuitBreakerMTSpec.openBreaker, see #2953