dont update nickname in old messages

Sometimes, depending on the context, I'll change my nickname in a server just to post a few messages with another handle, to make a point, a joke, etc.  This doesn't change old messages, which is good.  But if I change back to my original one, these new messages I've made with the temporary nickname will also change after a few minutes.

These messages should retain the temporary handle for affect, otherwise this new discordesque component is lost to the moment.