An lzw reader has dfferent behaviour whether the underlying reader is an io.ByteReader
or not.

http://play.golang.org/p/Z9ngQcpn8k

I was bitten by this when my tests used a bytes.Buffer (as in the provided code), but
the real code used an os.File.

The problem is that lzw.NewReader wraps the Reader in a bufio.Reader if the underlying
reader is not already a ByteReader. This bufio.Reader reads bytes following the
compressed data from the underlying Reader due to buffering, while the ByteReader does
not.

I'm not sure if this should be fixed, or merely documented.