add a couple of helper methods to io.ByteBuffer

R=rsc
DELTA=456  (9 added, 2 deleted, 445 changed)
OCL=23107
CL=23107

src/lib/io/bytebuffer.go

@@ -75,10 +75,18 @@ func (b *ByteBuffer) Len() int {
 	return b.len
 }
 
+func (b *ByteBuffer) Off() int {
+	return b.off
+}
+
 func (b *ByteBuffer) Data() []byte {
 	return b.buf[b.off:b.len]
 }
 
+func (b *ByteBuffer) AllData() []byte {
+	return b.buf[0:b.len]
+}
+
 
 export func NewByteBufferFromArray(buf []byte) *ByteBuffer {
 	b := new(ByteBuffer);