Fix changing client nick when client connects.

Fix changing client nick when client connects.

If nicks are equal, it's not changed. The problem was that equality was
checked case-insensitively.

This makes some clients which compare nicks case-sensitively think that
JOINs which we send to them, are not related to the user, it's someone
else joining. So Konversation users which have lower case version of
their IRC nick configured in Konversation settings, didn't get their
channel opened when connecting to ZNC.

Thanks to Axanon for helping to investigate the issue.