This was `.dealiasWiden`. I need to poke things a bit to see if that change makes sense.

In my poking, I've found a regression. It's not related to this line though (I tried reverting and it still failes)

```
object Test {
  type Id[X] = X
  val a: Id[Option[Int]] = None

  (a: a.type) match {
     case Some(x) => println(x)
     case None    =>
  }
}
```

```
% scalac-hash v2.11.0-M4 test/files/pos/t6771-singleton.scala
[info] v2.11.0-M4 => /Users/jason/usr/scala-v2.11.0-M4-0-g8b41240

% qbin/scalac test/files/pos/t6771-singleton.scala
test/files/pos/t6771-singleton.scala:6: error: constructor cannot be instantiated to expected type;
 found   : Some[A]
 required: Test.a.type
     case Some(x) => println(x)
          ^
test/files/pos/t6771.scala:6: error: not found: value x
     case Some(x) => println(x)
                             ^
two errors found

```