new bug: x, ok = t.m[i] doesn't compile

R=ken
OCL=13395
CL=13395

test/bugs/bug075.go

+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// 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 T struct { m *map[int]int }
+func main() {
+	t := new(T);
+	t.m = new(map[int]int);
+	var x int;
+	var ok bool;
+	x, ok = t.m[0];  //bug075.go:11: bad shape across assignment - cr=1 cl=2
+}