mime: fix RFC references

R=golang-dev, bradfitz
CC=brad fitzpatrick <bradfitz, golang-dev
https://golang.org/cl/4634063

src/pkg/mime/grammar.go

@@ -9,13 +9,13 @@ import (
 )
 
 // isTSpecial returns true if rune is in 'tspecials' as defined by RFC
-// 1531 and RFC 2045.
+// 1521 and RFC 2045.
 func isTSpecial(rune int) bool {
 	return strings.IndexRune(`()<>@,;:\"/[]?=`, rune) != -1
 }
 
 // IsTokenChar returns true if rune is in 'token' as defined by RFC
-// 1531 and RFC 2045.
+// 1521 and RFC 2045.
 func IsTokenChar(rune int) bool {
 	// token := 1*<any (US-ASCII) CHAR except SPACE, CTLs,
 	//             or tspecials>

src/pkg/mime/mediatype.go

@@ -31,7 +31,7 @@ func validMediaTypeOrDisposition(s string) bool {
 }
 
 // ParseMediaType parses a media type value and any optional
-// parameters, per RFC 1531.  Media types are the values in
+// parameters, per RFC 1521.  Media types are the values in
 // Content-Type and Content-Disposition headers (RFC 2183).  On
 // success, ParseMediaType returns the media type converted to
 // lowercase and trimmed of white space and a non-nil params.  On