Map Error Handling

While reviewing pull request https://github.com/Netflix/RxJava/pull/312 I noticed that the behavior of Map didn't seem right in how it continued emitting values and necessitated the changes to onErrorResumeNext. 

Digging in it seems the onNext was manually doing error handling but in a non-comprehensive manner whereas now I am letting the `SafeObserver` (previously called `AtomicObserver`) handle it which does unsubscribes and ignores subsequent events if it doesn't unsubscribe correctly.

This is also related to https://github.com/Netflix/RxJava/issues/216.