Change duplicate error message for missing irc.nick.
Add a 'VerboseReadLoop' option.

Troubleshooting responses from the IRC server becomes easier when
you can actually see the raw responses. This change adds a
'VerboseReadLoop' member to the Connection struct. When set to
true, the raw messages sent from the server will be placed into
the standard log for review. This message is printed before
evaluating any callbacks.
Add ReadLoop() debugging via Connection.Debug.
Merge pull request #45 from antzucaro/master

Add verbose logging for ReadLoop().