An unsubscribed AtomicObservableSubscription.wrap() unsubscribes its argument

[johngmyers]

Fixes #210

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[benjchristensen]

Interesting use case ... suggests either the wrap is being done at the wrong time or a race condition where a Subscription is being returned before a subscription is invoked - not sure when that would occur but there's probably some use case I'm not thinking of!

[johngmyers]

Per #210, the TestObservable sequence makes its last onNext() notification on another thread before TakeWhile.call() can stuff the ItemObserver's subscription into the AtomicObservableSubscription. Thus the AtomicObservableSubscription gets unsubscribed before the wrap() call.