Erroneous unreachable warning with path dependant type

```scala
class Foo {
  val bar = new Bar
  class Bar {
    sealed abstract class A
    case class B() extends A
    case class C() extends A
  }
}

class Test {
  val foo = new Foo
  import foo.bar._

  def test(a: A) = {
    a match {
      case B() => 1
      case _ => 2 // unreachable code
    }
  }
}
```