net/textproto: use ReadDotBytes instead of non-existent ReadDotAll.

Fixes #5893.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/13086043

src/pkg/net/textproto/textproto.go

@@ -105,7 +105,7 @@ func Dial(network, addr string) (*Conn, error) {
 //	if _, _, err = c.ReadCodeLine(110); err != nil {
 //		return nil, err
 //	}
-//	text, err := c.ReadDotAll()
+//	text, err := c.ReadDotBytes()
 //	if err != nil {
 //		return nil, err
 //	}