Register the connection with the IRC server.
        Required arguments:
        * nick - Nick to use. If a tuple/list is specified -
            it will try to use the first,
            and if the first is already used -
             it will try to use the second and so on.
        * user - Username to use.
        * real_name - Real name to use.
        Optional arguments:
        * password=None - IRC server password.

def _register(self, nick, user, real_name, password=None):
        """
        Register the connection with the IRC server.
        Required arguments:
        * nick - Nick to use. If a tuple/list is specified -
            it will try to use the first,
            and if the first is already used -
             it will try to use the second and so on.
        * user - Username to use.
        * real_name - Real name to use.
        Optional arguments:
        * password=None - IRC server password.
        """
        with self.lock:
            if password:
                self._password(password)

            self.nick(nick)
            self._user(user, real_name)