It has been a community request for a long time to have network specific nicks. Today, someone (kingkong) asked me about it while I wasn't doing anything, so I did it.
I added the configuration variable supybot.networks.XXX.nick, which defaults to empty value. If this variable is not empty, it will be used instead of supybot.nick. So, this patch does not break any configuration. I also updated Admin and NickCapture to use that new variable.