ChatChannel didn't return the message ID for sent messages, which made
using the returned ACKs impossible. The SendMessage method now returns
the uin32 messageID.
Also, SendMessage didn't support the TimeDelta field for messages, which
is used for queued or resent messages. This is now available as
SendMessageWithTime.
And finally, the ChatMessageAck callback didn't indicate if mesasges
were accepted or not, which is part of the protocol. That was added as a
field, which is unfortunately a breaking API change, but I've made
enough of those lately to not feel guilty about it.