mime: unexport some internal details

Fixes #2941

R=golang-dev, rsc, adg
CC=golang-dev
https://golang.org/cl/5663046

src/pkg/mime/grammar.go

@@ -14,25 +14,25 @@ func isTSpecial(r rune) bool {
 	return strings.IndexRune(`()<>@,;:\"/[]?=`, r) != -1
 }
 
-// IsTokenChar returns true if rune is in 'token' as defined by RFC
+// isTokenChar returns true if rune is in 'token' as defined by RFC
 // 1521 and RFC 2045.
-func IsTokenChar(r rune) bool {
+func isTokenChar(r rune) bool {
 	// token := 1*<any (US-ASCII) CHAR except SPACE, CTLs,
 	//             or tspecials>
 	return r > 0x20 && r < 0x7f && !isTSpecial(r)
 }
 
-// IsToken returns true if s is a 'token' as as defined by RFC 1521
+// isToken returns true if s is a 'token' as as defined by RFC 1521
 // and RFC 2045.
-func IsToken(s string) bool {
+func isToken(s string) bool {
 	if s == "" {
 		return false
 	}
 	return strings.IndexFunc(s, isNotTokenChar) < 0
 }
 
-// IsQText returns true if rune is in 'qtext' as defined by RFC 822.
-func IsQText(r int) bool {
+// isQText returns true if rune is in 'qtext' as defined by RFC 822.
+func isQText(r int) bool {
 	// CHAR        =  <any ASCII character>        ; (  0-177,  0.-127.)
 	// qtext       =  <any CHAR excepting <">,     ; => may be folded
 	//                "\" & CR, and including

src/pkg/mime/mediatype.go

@@ -23,7 +23,7 @@ func FormatMediaType(t string, param map[string]string) string {
 		return ""
 	}
 	major, sub := t[:slash], t[slash+1:]
-	if !IsToken(major) || !IsToken(sub) {
+	if !isToken(major) || !isToken(sub) {
 		return ""
 	}
 	var b bytes.Buffer
@@ -34,12 +34,12 @@ func FormatMediaType(t string, param map[string]string) string {
 	for attribute, value := range param {
 		b.WriteByte(';')
 		b.WriteByte(' ')
-		if !IsToken(attribute) {
+		if !isToken(attribute) {
 			return ""
 		}
 		b.WriteString(strings.ToLower(attribute))
 		b.WriteByte('=')
-		if IsToken(value) {
+		if isToken(value) {
 			b.WriteString(value)
 			continue
 		}
@@ -205,7 +205,7 @@ func decode2231Enc(v string) string {
 }
 
 func isNotTokenChar(r rune) bool {
-	return !IsTokenChar(r)
+	return !isTokenChar(r)
 }
 
 // consumeToken consumes a token from the beginning of provided