added regression test for t301

git-svn-id: http://lampsvn.epfl.ch/svn-repos/scala/scala/trunk@13657 5e8d7ff9-d8ef-0310-90f0-a4852d11357a

test/files/pos/t301.scala

@@ -0,0 +1,12 @@
+package fos
+
+abstract class Expr
+case class Var extends Expr
+
+object Analyzer {
+  def substitution(expr: Expr, cls: (Var,Var)): Expr =
+    expr match {
+      case cls._2 => cls._1  // source of the error
+      case _ => expr
+    }
+}