Compilation fixes

... missed these when doing https://github.com/Netflix/Hystrix/commit/00d8ecb9c87c35e91a2b1a696ea92c8ffb8121ad#diff-bcc766d81acc427070683ec44e8320c2
Merge pull request #262 from benjchristensen/compilation-fix

Compilation fixes
New signature for HystrixObservableCollapser

Replacing mapResponseToRequests with functional style selectors and allowing streaming response from Observable.
Javadoc for new HystrixObservableCollapser methods