Zip with Backpressure Support

This supports both upstream and downstream backpressure.
New test case for takeWhile that currently fails
Fix issue #1451
Fix related classes for issue #1451
OperatorAll & Backpressure

Similar to filter, it needs to request(1) each time it filters an onNext.
Debugging Test
Merge pull request #1446 from benjchristensen/zip-backpressure

Zip with Backpressure Support
Merge pull request #1454 from zsxwing/issue1451

Fix issue #1451
Merge pull request #1453 from spodila/takeWhileFailure

New test case for takeWhile that currently fails
Removing onSetProducer from the API
MergeDelayError & OnErrorFlatMap w/ Merge
Merge pull request #1457 from benjchristensen/mergeDelayError-backpressure

MergeDelayError & OnErrorFlatMap w/ Merge
Remove test ... leave functional testing in core

The behavior of mergeDelayError has slightly changed.

It doesn't eagerly unsubscribe if the source keeps emitting after onError.
Removing unnecessary test
Removing unnecessary test
Remove Pivot Operator

as per https://github.com/Netflix/RxJava/issues/1402
Merge pull request #1458 from benjchristensen/remove-pivot

Remove Pivot Operator
Merge branch 'remove-onsetproducer' of github.com:abersnaze/RxJava into remove-onSetProducer
Support OnSetProducer/Request Changes
Merge pull request #1459 from benjchristensen/remove-onSetProducer

Remove Subscriber.onSetProducer