Erasure doesn't insert all box\unbox corsions for ifs

```
    def id[T](t: T) = t
    { if (x) id(one) else 0} + 1
    { if (x) new scala.util.Random()}.asInstanceOf[Runnable]
```

After erasure both those if's have different types of branches:

```
    { if (x) id(box(one)) else 0} + 1
    { if (x) new scala.util.Random() else ()}.asInstanceOf[Runnable]
```

In first example `id` should get unboxed,
In the second example `()` should get boxed.
