update ChunkedFile to seekable reader, so we can use io.* to read data

go/storage/needle_read_write.go

@@ -16,7 +16,7 @@ const (
 	FlagHasMime             = 0x04
 	FlagHasLastModifiedDate = 0x08
 	FlagHasTtl              = 0x10
-	FlagChunkList           = 0x80
+	FlagChunkedFile         = 0x80
 	LastModifiedBytesLength = 5
 	TtlBytesLength          = 2
 )
@@ -282,10 +282,10 @@ func (n *Needle) SetHasTtl() {
 	n.Flags = n.Flags | FlagHasTtl
 }
 
-func (n *Needle) IsChunkList() bool {
-	return n.Flags&FlagChunkList > 0
+func (n *Needle) IsChunkedFile() bool {
+	return n.Flags&FlagChunkedFile > 0
 }
 
-func (n *Needle) SetChunkList() {
-	n.Flags = n.Flags | FlagChunkList
+func (n *Needle) SetChunkedFile() {
+	n.Flags = n.Flags | FlagChunkedFile
 }