Fix all of the include guards for all of the headers.

Also fix copyright statements in headers.
Ah, didn't read down this far before my comment on top file, GPL guidance says we have to list all contributors with years of contributions - which helps to prove that those contributions are released within the scope of the GPL.  I still think we have to do something about the large amount of both core and add-on bits of Lua which is (all I hope) under a 3-clause MIT licence. That is *explicitly known* to be compatible in terms with GPL but I'm sure that we do have to say somewhere that it was licensed - I think I have better put another tab onto the "About Mudlet" dialog to show this: [Lua Licence](http://www.lua.org/license.html).