OperatorDoOnRequest.ParentSubscriber should be static class
Fix the issue that map may swallow fatal exceptions
enable faster travis builds
Merge pull request #2156 from zsxwing/map-swallow-fatal-exceptions

Fix the issue that map may swallow fatal exceptions
Merge pull request #2052 from davidmoten/make-class-static

OperatorDoOnRequest.ParentSubscriber should be static class
RxRingBuffer with Inline Release

Can release when ...

- terminal event emitted
- unsubscribe/release occurs and queue is empty
- unsubscribe/release has occurred and poll/peek occurs

Can result in a queue not being put back in the pool if an early unsubscribe occurs from a different thread and causes the poll/peek to not trigger the release. In this case GC will reclaim the pool so it still functions, it just misses the pooling optimization.

There is a commented out test of using finalize(). It works as a safety net for the edge case, but at the cost of increased GC time.