Unable to rename re-exported identifiers

VS2015

**TypeScript Version:** 

1.8.6

**Code**

Rename `var a` to `var c` in `a.ts`.

``` ts
// a.ts
export var a;
// b.ts
import {a} from './a';
export {a}
```

**Expected behavior:**

``` ts
import {c} from './a';
export {c}
```

**Actual behavior:** 

``` ts
import {c} from './a';
export {a}
```
