Remove Trailing param

[DanielOaks]

Trailing itself shouldn't be exposed as separate from the parameters. This is because the trailing param is just a syntax hack to let the last parameter contain spaces.

As an example, these two lines are functionally identical in the IRC protocol, and both forms can be emitted by servers:

TOPIC #testchan cooltopic
TOPIC #testchan :cooltopic

In the first line, cooltopic is not trailing (since it doesn't need to be), and in the second one cooltopic is trailing. In this case, Dispatch currently fails to correctly display this. It also does the same on this for Privmsgs and such.

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If using the msg.Params[len(msg.Params)-1] syntax everywhere is ugly we could always replace it with something like msg.LastParam and make sure that the last parameter is always copied into it, but I'm iffy on that since it's duplicating info.

[khlieng]

Awesome, thanks!