fix(catch): fix catch() to preserve Subscriber chain

Fix Catch() operator to include CatchSubscriber in the destination Subscriber, in order not to break
unsubscription chains.

Author: staltz

src/operator/catch.ts

@@ -39,6 +39,7 @@ class CatchSubscriber<T> extends Subscriber<T> {
               private caught: Observable<any>) {
     super(null);
     this.lastSubscription = this;
+    this.destination.add(this);
   }
 
   _next(value: T) {