evaluating a disposed deferred dependentObservable causes it to take dependencies

If I create a dependantObservable with `deferEvaluation: true`, and then dispose of it before ever evaluating it, and then finally evaluate it, it ends up taking dependencies:

```
var o = ko.observable(42);
var c = ko.computed({ read: o, deferEvaluation: true });

c.dispose();
c(); // takes dependency on o here
```

If I change `deferEvalutation` to false then no dependencies get taken.

Here is a [jsFiddle](http://jsfiddle.net/9Nmyq/) showing the issue.