CLOSE_WAIT sockets issue fixed. Decoder must always calls decoder_error() in
any error condition to be sure that all the splices and connections are dropped.

The following conditions produced CLOSE_WAIT sockets in my tests:

- The client connected to the Wanproxy client resets the connections instead of
 closing it cleanly.
- At (almost) the same time (but a few milliseconds before) the server where
 Wanproxy server is connected closes the connection cleanly.
- The WP server sends the EOS/EOS_ACK exchange.
- The WP Client closes the connection without doing the EOS/EOS_ACK exchange.
- The server side is never noticed of the connection closed under this condition.