Make irc module accept the nick being shortened by the server.

This can happen if the server has a NICKLEN setting which is less
than the length of the specified nick. With this patch we now grab
that nick and use it moving forward, instead of failing because we
didn't get back the one we specified, in the connection response.
Fix whitespace (tabs -> spaces).
Merge pull request #6289 from rawtaz/fix-irc-nicklen

Make irc module accept the nick being shortened by the server.