Ignore furthur messages after entering terminate state
Error Handling Unsubscribe and Terminal State
Make TakeUntil obey Rx contract
[Gradle Release Plugin] - pre tag commit:  '0.20.4'.
[Gradle Release Plugin] - new version commit:  '0.20.5-SNAPSHOT'.
0.20.4
rewrite OnSubscribeRefCount to handle synchronous source, add null check to OperatorMulticast