fix(switchMapTo): reimplement switchMapTo to pass tests
fix(switchMapTo): reimplement switchMapTo to pass tests

Rewrite switchMapTo operator, which was previously behaving just like
concatMapTo, because it reused mergeMapTo behavior, with concurrency
parameter=1.

figueredo/RxJS,SangKa/RxJS-Docs-CN,justinwoo/RxJS,trxcllnt/RxJS,jinroh/RxJS,martinsik/rxjs,staltz/RxJSNext,staltz/RxJSNext,gluck/RxJS,figueredo/RxJS,robwormald/RxJS,robwormald/RxJS,SangKa/RxJS-Docs-CN,figueredo/RxJS,RxJS-CN/RxJS-Docs-CN,ReactiveX/rxjs,mattpodwysocki/RxJS,elliotschi/rxjs,IgorMinar/RxJS,ReactiveX/RxJS,adrianomelo/RxJS-1,gluck/RxJS,SangKa/RxJS-Docs-CN,jadbox/RxJS,kwonoj/RxJS,trxcllnt/RxJS,benlesh/RxJS,RxJS-CN/RxJS-Docs-CN,ReactiveX/RxJS,Brocco/RxJS,adrianomelo/RxJS-1,adrianomelo/RxJSNext,jayphelps/rxjs,mattpodwysocki/RxJS,Brocco/RxJS,justinwoo/RxJS,jayphelps/rxjs,Igorbek/rxjs5,martinsik/rxjs,Igorbek/rxjs5,jadbox/RxJS,jayphelps/rxjs,ReactiveX/rxjs,adrianomelo/RxJS-1,ReactiveX/RxJS,adrianomelo/RxJSNext,jayphelps/rxjs,jinroh/RxJS,gluck/RxJS,kwonoj/RxJS,RxJS-CN/RxJS-Docs-CN,ReactiveX/rxjs,benlesh/RxJS,martinsik/rxjs,RxJS-CN/RxJS-Docs-CN,elliotschi/rxjs,martinsik/rxjs,ReactiveX/RxJS,kwonoj/RxJS,saneyuki/RxJS,benlesh/RxJS,adrianomelo/RxJSNext,kwonoj/RxJS,figueredo/RxJS,jadbox/RxJS,staltz/RxJSNext,mattpodwysocki/RxJS,robwormald/RxJS,justinwoo/RxJS,Brocco/RxJS,saneyuki/RxJS,trxcllnt/RxJS,IgorMinar/RxJS,adrianomelo/RxJS-1,elliotschi/rxjs,benlesh/RxJS,adrianomelo/RxJSNext,ReactiveX/rxjs,jinroh/RxJS,staltz/RxJSNext,jinroh/RxJS,SangKa/RxJS-Docs-CN,robwormald/RxJS,elliotschi/rxjs,Brocco/RxJS,jadbox/RxJS,jayphelps/rxjs,trxcllnt/RxJS,gluck/RxJS,mattpodwysocki/RxJS,Igorbek/rxjs5,Igorbek/rxjs5,justinwoo/RxJS