OperationTakeWhile doesn't protect calls to predicate

[johngmyers]

Per RX guideline 6.4, calls to selector functions passed in to the operator should be caught and fed through to the subscribed observer. Operator TakeWhile doesn't do this with the passed in predicate.

        @Test
        public void testTakeWhileProtectsPredicateCall() {
            TestObservable source = new TestObservable(mock(Subscription.class), "one");
            final RuntimeException testException = new RuntimeException("test exception");

            @SuppressWarnings("unchecked")
            Observer<String> aObserver = mock(Observer.class);
            Observable<String> take = Observable.create(takeWhile(source, new Func1<String, Boolean>()
            {
                @Override
                public Boolean call(String s)
                {
                    throw testException;
                }
            }));
            take.subscribe(aObserver);

            // wait for the Observable to complete
            try {
                source.t.join();
            } catch (Exception e) {
                e.printStackTrace();
                fail(e.getMessage());
            }

            verify(aObserver, never()).onNext(any(String.class));
            verify(aObserver, times(1)).onError(testException);
        }

[johngmyers]

Might as well supply the fix. Sent pull #220.