http: Allow cookies with negative Max-Age attribute as these are

allowed by RFC 6265 sec 5.2.2.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5533083

src/pkg/net/http/cookie.go

@@ -96,7 +96,7 @@ func readSetCookies(h Header) []*Cookie {
 				continue
 			case "max-age":
 				secs, err := strconv.Atoi(val)
-				if err != nil || secs < 0 || secs != 0 && val[0] == '0' {
+				if err != nil || secs != 0 && val[0] == '0' {
 					break
 				}
 				if secs <= 0 {