net/proto2/go: make a slight change to how we handle []byte fields

This is meant to fix https://github.com/golang/protobuf/pull/188. There
are no tests because we don't guarantee that we're going to maintain
this behavior in the future.

Fixes #188

jsonpb/jsonpb.go

diff --git a/jsonpb/jsonpb.go b/jsonpb/jsonpb.go
index 71985e6..0ad60eb 100644
--- a/jsonpb/jsonpb.go
+++ b/jsonpb/jsonpb.go
@@ -53,10 +53,6 @@
 	"github.com/golang/protobuf/proto"
 )
 
-var (
-	byteArrayType = reflect.TypeOf([]byte{})
-)
-
 // Marshaler is a configurable object for converting between
 // protocol buffer objects and a JSON representation for them.
 type Marshaler struct {
@@ -374,7 +370,7 @@
 	v = reflect.Indirect(v)
 
 	// Handle repeated elements.
-	if v.Type() != byteArrayType && v.Kind() == reflect.Slice {
+	if v.Kind() == reflect.Slice && v.Type().Elem().Kind() != reflect.Uint8 {
 		out.write("[")
 		comma := ""
 		for i := 0; i < v.Len(); i++ {
@@ -684,7 +680,7 @@
 	}
 
 	// Handle arrays (which aren't encoded bytes)
-	if targetType != byteArrayType && targetType.Kind() == reflect.Slice {
+	if targetType.Kind() == reflect.Slice && targetType.Elem().Kind() != reflect.Uint8 {
 		var slc []json.RawMessage
 		if err := json.Unmarshal(inputValue, &slc); err != nil {
 			return err

proto/text.go

diff --git a/proto/text.go b/proto/text.go
index bd6f1ae..8214ce3 100644
--- a/proto/text.go
+++ b/proto/text.go
@@ -513,7 +513,7 @@
 	switch v.Kind() {
 	case reflect.Slice:
 		// Should only be a []byte; repeated fields are handled in writeStruct.
-		if err := writeString(w, string(v.Interface().([]byte))); err != nil {
+		if err := writeString(w, string(v.Bytes())); err != nil {
 			return err
 		}
 	case reflect.String: