Unwrap errors properly for patform specific connection retry code.

Include more possible errors for Windows.

For #442

fs/closed_conn_win.go

@@ -16,8 +16,15 @@ func isClosedConnErrorPlatform(err error) bool {
 	if oe, ok := err.(*net.OpError); ok {
 		if se, ok := oe.Err.(*os.SyscallError); ok {
 			if errno, ok := se.Err.(syscall.Errno); ok {
-				const WSAECONNABORTED syscall.Errno = 10053
-				if errno == syscall.WSAECONNRESET || errno == WSAECONNABORTED {
+				const (
+					WSAECONNABORTED   syscall.Errno = 10053
+					WSAHOST_NOT_FOUND syscall.Errno = 11001
+					WSATRY_AGAIN      syscall.Errno = 11002
+					WSAENETRESET      syscall.Errno = 10052
+					WSAETIMEDOUT      syscall.Errno = 10060
+				)
+				switch errno {
+				case syscall.WSAECONNRESET, WSAECONNABORTED, WSAHOST_NOT_FOUND, WSATRY_AGAIN, WSAENETRESET, WSAETIMEDOUT:
 					return true
 				}
 			}

fs/error.go

@@ -8,6 +8,8 @@ import (
 	"net/http"
 	"net/url"
 	"strings"
+
+	"github.com/pkg/errors"
 )
 
 // Retry is an optional interface for error as to whether the
@@ -95,16 +97,19 @@ func ShouldRetry(err error) bool {
 		return false
 	}
 
-	// Look for premature closing of connection
-	if err == io.EOF || err == io.ErrUnexpectedEOF || isClosedConnError(err) {
-		return true
-	}
+	// Find root cause if available
+	err = errors.Cause(err)
 
 	// Unwrap url.Error
 	if urlErr, ok := err.(*url.Error); ok {
 		err = urlErr.Err
 	}
 
+	// Look for premature closing of connection
+	if err == io.EOF || err == io.ErrUnexpectedEOF || isClosedConnError(err) {
+		return true
+	}
+
 	// Check for net error Timeout()
 	if x, ok := err.(interface {
 		Timeout() bool