added test for KT-239

idea/testData/codegen/regressions/kt239.jet

@@ -0,0 +1,3 @@
+fun box(i: Int?) {
+    val j = i?.plus(3) //verify error
+}

idea/tests/org/jetbrains/jet/codegen/PrimitiveTypesTest.java

@@ -262,4 +262,8 @@ public class PrimitiveTypesTest extends CodegenTestCase {
     public void testKt242 () throws Exception {
         blackBoxFile("regressions/kt242.jet");
     }
+
+    public void testKt239 () throws Exception {
+        blackBoxFile("regressions/kt242.jet");
+    }
 }