Tweak logic for hk type comparisons

Author: odersky

tests/pos/i2200/Hello.scala

@@ -0,0 +1,6 @@
+package bar
+import scala.language.higherKinds
+class Fix[F[_]](unfix: F[Fix[F]])
+object DocTree {
+  def docTree(s: StreamTree[DocTree]): DocTree = new Fix(s: StreamTree[DocTree])
+}

tests/pos/i2200/package.scala

@@ -0,0 +1,4 @@
+package object bar {
+  type StreamTree[T] = Stream[Int]
+  type DocTree = Fix[StreamTree]
+}