Observable+throttleFirst.swift

extension ObservableType {
    /**
    throttleFirst

    RxJava reference
    http://reactivex.io/RxJava/javadoc/rx/Observable.html#throttleFirst(long,%20java.util.concurrent.TimeUnit,%20rx.Scheduler)
    */
    func throttleFirst(time: RxTimeInterval, scheduler: SchedulerType) -> Observable<E> {
        let s = self.share()

        return s
            .throttle(time, scheduler: scheduler)
            .map { _ in () }
            .startWith()
            .flatMapLatest{ _ in s.take(1) }
    }
}