Access written message from WriteCompletionEvent

[Sai Pullabhotla]

Is there a good reason why the WriteCompletionEvent does not provide
access to the message that was written? I did see the JIRA case at
https://jira.jboss.org/browse/NETTY-118. It said that the handler
implementation becomes complicated. I'm not sure how complicated it
would be, but for ease of use of the API, it would be nice to have the
message available. This is especially useful for logging purposes to
log only those messages that were actually sent.