Export of not initialized variable and useless statement

TS code:

``` typescript
module myModule {
    export var a: number = 1;
    export var b: number;
}
```

Compiled to: 

``` javascript
var myModule;
(function (myModule) {
    myModule.a = 1;
    myModule.b;
})(myModule || (myModule = {}));
```

The statement `myModule.b` is useless.
