gc: allow ... in method lists

R=ken2
https://golang.org/cl/179070

src/cmd/gc/go.y

@@ -1285,7 +1285,7 @@ indcl:
 	'(' oarg_type_list_ocomma ')' fnres
 	{
 		// without func keyword
-		$2 = checkarglist($2, 0);
+		$2 = checkarglist($2, 1);
 		$$ = nod(OTFUNC, fakethis(), N);
 		$$->list = $2;
 		$$->rlist = $4;

test/fixedbugs/bug232.go

+// $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 I interface { X(...) }