test(filter): test the number of calls to the predicate function
test(filter): test the number of calls to the predicate function

relates to #390.

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