Property assignments in constructor should show up in intellisense

If you request completion at the `/**/` below...

``` ts
class C {
  constructor() {
    this.x = 'foo';
  }
}
let c = new C();
c./**/;
```

**Expected behavior:**

Completion list should contain `x`.

**Actual behavior:** 

Completion list does not contain `x`.

Currently there is an error at `this.x = 'foo'`, "Property 'x' does not exist in 'C'". That error should stay.
