test: Add test for inheriting private method from anonymous field.

The spec says that all methods are inherited from an anonymous
field.  There is no exception for non-exported methods.

This is related to issue 1536.

R=rsc
CC=golang-dev
https://golang.org/cl/5012043

test/bugs/bug367.dir/main.go

+package main
+
+import (
+	"./p"
+)
+
+type T struct{ *p.S }
+
+func main() {
+	var t T
+	p.F(t)
+}

test/bugs/bug367.dir/p.go

+package p
+
+type T struct{ x int }
+type S struct{}
+
+func (p *S) get() T {
+	return T{0}
+}
+
+type I interface {
+	get() T
+}
+
+func F(i I) {
+	_ = i.get()
+}

test/bugs/bug367.go

+// $G $D/$F.dir/p.go && $G $D/$F.dir/main.go && $L main.$A && ./$A.out || echo BUG: should not fail
+
+// Copyright 2011 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.
+
+ignored

test/golden.out

@@ -155,3 +155,7 @@ panic: interface conversion: interface is main.T, not main.T
 0x0
 
 == bugs/
+
+=========== bugs/bug367.go
+panic: interface conversion: main.T is not p.I: missing method get
+BUG: should not fail