Don't put utf8 in such a privileged position.

[barrucadu]

It's a sensible default, but right now it's impossible to use irc-client with things that aren't utf-8!

[barrucadu]

There are a couple of issues here:

1. irc-ctcp only has a nice decoder to Text (but that can be remedied with a small function)
2. matchCTCP is currently case-insensitive, but if it operates on an arbitrary ByteString it doesn't know enough to be able to do that.
3. nickMangler assumes the character encoding of the nick is known, so that it can substitute characters.