go.text/language: make it build with Go 1.1, which does not include

sort.Stable.

Fixes golang/go#6523.

R=r
CC=golang-dev
https://golang.org/cl/14265043

Author: mpvl

language/go1_1.go

@@ -0,0 +1,38 @@
+// Copyright 2013 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.
+
+// +build !go1.2
+
+package language
+
+import "sort"
+
+func sortStable(s sort.Interface) {
+	ss := stableSort{
+		s:   s,
+		pos: make([]int, s.Len()),
+	}
+	for i := range ss.pos {
+		ss.pos[i] = i
+	}
+	sort.Sort(&ss)
+}
+
+type stableSort struct {
+	s   sort.Interface
+	pos []int
+}
+
+func (s *stableSort) Len() int {
+	return len(s.pos)
+}
+
+func (s *stableSort) Less(i, j int) bool {
+	return s.s.Less(i, j) || !s.s.Less(j, i) && s.pos[i] < s.pos[j]
+}
+
+func (s *stableSort) Swap(i, j int) {
+	s.s.Swap(i, j)
+	s.pos[i], s.pos[j] = s.pos[j], s.pos[i]
+}

language/go1_2.go

@@ -0,0 +1,11 @@
+// Copyright 2013 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.
+
+// +build go1.2
+
+package language
+
+import "sort"
+
+var sortStable = sort.Stable

language/parse.go

@@ -595,7 +595,7 @@ func ParseAcceptLanguage(s string) (tag []Tag, q []float32, err error) {
 			q = append(q, float32(w))
 		}
 	}
-	sort.Stable(&tagSort{tag, q})
+	sortStable(&tagSort{tag, q})
 	return tag, q, nil
 }