Add a test for issue 337.

gccgo currently miscompiles this test.

R=rsc
CC=golang-dev
https://golang.org/cl/181050

test/fixedbugs/bug237.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
+
+import "fmt"
+
+var indent uint = 10
+func main() {
+	const dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " +
+		". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
+	const n = uint(len(dots))
+	i := 2 * indent
+	var s string
+	for ; i > n; i -= n {
+		s += fmt.Sprint(dots)
+	}
+	s += dots[0:i]
+	if s != ". . . . . . . . . . " {
+		panic(s)
+	}
+}