GADT test

This one failed in getters before because a (previously unchecked) assignment
was turned into a checked application. Now it passes.

Author: odersky

tests/pending/pos/gadts2.scala renamed to tests/pos/gadts2.scala

@@ -8,9 +8,9 @@ object Test {
   case class Cell[a](var x: a) extends Term[a]
   final case class NumTerm(val n: Number) extends Term[Number]
 
-  def f[a](t: Term[a], c: Cell[a]): Unit = {
+  def f[A](t: Term[A], c: Cell[A]): Unit = {
     t match {
-      case NumTerm(n) => c.x = MyDouble(1.0)
+      case NumTerm(n) => c.x = MyDouble(1.0)  // problem is: this assignment is not type correct, since gadt variable is forgotten
     }
   }