RxJS patch is not closure safe

[mhevery]

1. Assignment into imported constructor is not allowed: https://github.com/angular/zone.js/blob/master/lib/rxjs/rxjs.ts#L75
2. We can’t use string literals here: https://github.com/angular/zone.js/blob/master/lib/rxjs/rxjs.ts#L230 since they don’t minify in closure

The fix for #1 is https://github.com/trxcllnt/rxjs/blob/53eddb1cca1228fe6d81aa6bec0ee0a57c8f4664/src/add/zone.ts#L60-L74 The trick is to intercept the setter to have side-effects. This way we don’t need to replace the constructor.

[JiaLiPassion]

@mhevery , I have modified this one in #848, please review.