agressively cleanup references at release

common/io/buffered_reader.go

@@ -22,6 +22,8 @@ func NewBufferedReader(rawReader io.Reader) *BufferedReader {
 
 func (this *BufferedReader) Release() {
 	this.buffer.Release()
+	this.buffer = nil
+	this.reader = nil
 }
 
 func (this *BufferedReader) Cached() bool {

common/io/buffered_writer.go

@@ -60,4 +60,6 @@ func (this *BufferedWriter) SetCached(cached bool) {
 
 func (this *BufferedWriter) Release() {
 	this.buffer.Release()
+	this.buffer = nil
+	this.writer = nil
 }