RFC-6143 ClientCutText/ServerCutText doesn't work

[andrews239]

Expects the wrong numbers for Bell/ServerCutText in a message from a server to the client.

asyncvnc.py:

    #: Clipboard update.
    CLIPBOARD = 2

     #: Bell update.
    BELL = 3

RFC-6143:

[7.6]  Server-to-Client Messages

   The server-to-client message types defined in this document are:

                      +--------+--------------------+
                      | Number | Name               |
                      +--------+--------------------+
                      | 0      | FramebufferUpdate  |
                      | 1      | SetColorMapEntries |
                      | 2      | Bell               |
                      | 3      | ServerCutText      |
                      +--------+--------------------+

Makes the wrong padding in a clipboard update message from the client to a server.
asyncvnc.py:

        self.writer.write(b'\x06\x00' + len(data).to_bytes(4, 'big') + data)

RFC-6143:

[7.5.6]  ClientCutText
              +--------------+--------------+--------------+
              | No. of bytes | Type [Value] | Description  |
              +--------------+--------------+--------------+
              | 1            | U8 [6]       | message-type |
              | 3            |              | padding      |
              | 4            | U32          | length       |
              | length       | U8 array     | text         |
              +--------------+--------------+--------------+

With any Bell/CutText message, the server and client sides become discouraged.