encoding/gob: fix bug in Register

The old code added a star but did not indirect the reflect.Type.

R=bradfitz
CC=golang-dev
https://golang.org/cl/6348067

src/pkg/encoding/gob/type.go

@@ -755,7 +755,7 @@ func Register(value interface{}) {
 	if rt.Name() == "" {
 		if pt := rt; pt.Kind() == reflect.Ptr {
 			star = "*"
-			rt = pt
+			rt = pt.Elem()
 		}
 	}
 	if rt.Name() != "" {