add doubled labels test case

Change-Id: I82d3c5c2ef73e026347e94df9a499ba714f5e971

src/internal/types/testdata/check/doubled_labels.go

@@ -0,0 +1,26 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+func _() {
+outer:
+inner:
+	for {
+		continue inner
+		break inner
+	}
+	goto outer
+}
+
+func _() {
+outer:
+inner:
+	for {
+		continue inner
+		continue outer /* ERROR "invalid continue label outer" */
+		break outer    /* ERROR "invalid break label outer" */
+	}
+	goto outer
+}