Instanceof in type guards should not narrow any

Usually narrowing a type causes us to have access to more properties. Not so if the original type was any. In this case, narrowing actually causes us to _lose_ properties. So we should not get an error in the following case:

``` ts
var x: any = { p: 0 };
if (x instanceof Object) {
    x.p; // Error that p does not exist on Object
}
```
