http: make Transport warning about connections closing more accurate

It was fragile and non-portable, and then became spammy with
the os.EINVAL removal.  Now it just uses the length of the
Peek return value instead.

R=golang-dev, alex.brainman
CC=golang-dev
https://golang.org/cl/5453065

src/pkg/net/http/Makefile

@@ -21,9 +21,4 @@ GOFILES=\
 	transfer.go\
 	transport.go\
 
-GOFILES_windows=\
-	transport_windows.go\
-
-GOFILES+=$(GOFILES_$(GOOS))
-
 include ../../../Make.pkg

src/pkg/net/http/transport.go

@@ -519,17 +519,11 @@ func (pc *persistConn) readLoop() {
 
 	for alive {
 		pb, err := pc.br.Peek(1)
-		if err != nil {
-			if remoteSideClosed(err) && !pc.expectingResponse() {
-				// Remote side closed on us.  (We probably hit their
-				// max idle timeout)
-				pc.close()
-				return
-			}
-		}
 		if !pc.expectingResponse() {
+			if len(pb) > 0 {
 				log.Printf("Unsolicited response received on idle HTTP channel starting with %q; err=%v",
 					string(pb), err)
+			}
 			pc.close()
 			return
 		}

src/pkg/net/http/transport_windows.go

-// 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.
-
-package http
-
-import (
-	"net"
-	"syscall"
-)
-
-func init() {
-	remoteSideClosedFunc = func(err error) (out bool) {
-		op, ok := err.(*net.OpError)
-		if ok && op.Op == "WSARecv" && op.Net == "tcp" && op.Err == syscall.Errno(10058) {
-			// TODO(brainman,rsc): Fix whatever is generating this.
-			return true
-		}
-		return false
-	}
-}