test(repeat): add test against breaking unsubscription chain
test(repeat): add test against breaking unsubscription chain

Add test for repeat() operator to verify that unsubscription chains are not broken when unsubscribe
happens.

For issue #875.

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