Fix Rx serialization bug in takeUntil again
Fix the race condition in BufferUntilSubscriber
Use EmptyObserver instead of Subscribers.empty()

onError should be ignored after unsubscribe is called.
Fix the compose generics
Fix the compose generics in RxScala
Added a unit test to demonstrate regression in Observable.mergeDelayError
Fix the failing Observable.mergeDelayError synchronous error unit test
Merge pull request #1712 from mattrjacobs/demonstrate-mergeDelayError-regression

Fixing regression in mergeDelayError
Merge pull request #1701 from zsxwing/compose-generics

Fix the compose generics
Merge pull request #1686 from zsxwing/fix-takeUntil

Fix Rx serialization bug in takeUntil again and the concurrent issue in BufferUntilSubscriber
Deprecate Parallel

see https://github.com/ReactiveX/RxJava/issues/1673
Merge pull request #1715 from benjchristensen/deprecate-parallel

Deprecate Parallel
[Gradle Release Plugin] - pre tag commit:  '0.20.5'.
[Gradle Release Plugin] - new version commit:  '0.20.6-SNAPSHOT'.
0.20.5
Bug in the onBackpressure operators
Merge pull request #1721 from abersnaze/onBackpressure-request-max-0.20

Bug in the onBackpressure operators