Add test for structural types

Author: liufengyun

tests/init/neg/structural.scala

@@ -0,0 +1,12 @@
+import reflect.Selectable.reflectiveSelectable
+
+class Test {
+  trait A
+  val m: A { def apply(x: Int): Int } =
+    new A {
+      def apply(x: Int): Int =
+        n + x
+    }
+
+  val n = m(23)   // error
+}