bug 211: duplicate interface methods not caught by 6g

R=gri
DELTA=17  (17 added, 0 deleted, 0 changed)
OCL=35852
CL=35876
diff --git a/test/bugs/bug211.go b/test/bugs/bug211.go
new file mode 100644
index 0000000..69aeeee
--- /dev/null
+++ b/test/bugs/bug211.go
@@ -0,0 +1,14 @@
+// errchk $G $D/$F.go
+
+// Copyright 2009 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 main
+
+type R interface { duplicate() }
+type S interface { duplicate() }
+type T interface { R; S }	// ERROR "duplicate"
+
+func main() {
+}