Fixing ipv6 parsing and messages with colons in them.

As mentioned in https://github.com/martynsmith/node-irc/commit/af75124b18652ea7bbb14b8127fc545404791a32#commitcomment-1956569 this commits breaks messages containing colons anywhere. As you can see in the image below this is parsed using irc.js with that version, it also occasionally crashes on ipv6.

![1cQK5](https://f.cloud.github.com/assets/45660/45178/87bf1cd8-5751-11e2-8c82-8276edb8cf72.png)

I've managed to fix it by checking for a space then a colon, as per the IRC RFC http://www.ietf.org/rfc/rfc1459.txt a colon has to be preceded by a space and as far as I know always is because the command is delimited by spaces. So theres no reason for any fancy regex, we can just force a space in at the start if needed and then look for ' :' because an ipv6 hostname can't contain any spaces.

Please review!