[Azoth Xoox] RoomPublicMessage::SetParticipantEntry().
[Azoth Xoox] GlooxMessage::SetVariant().
[Azoth Xoox] RoomParticipantEntry::StealMessagesFrom().
[Azoth Xoox] RoomCLEntry::MoveMessages().
[Azoth Xoox] Make rename messages children of new nick.
[Azoth Xoox] Proper merging logic for MUC nick changes.

If someone changes nick to a nick that's already present in a MUC room,
new chat entry gets overwritten by the old one, possibly leaving
dangling pointers. Just merge the messages from two items into one.
[Azoth Xoox] Code style fixes.
[Azoth Xoox] More code style fixes.
[Juffed] Removed useless dumb stub.