This is Will Fitzgerald. I wrote spec, but haven't been writing any arc code recently. I put Spec under the artistic license because that it what Arc used. I would be glad to offer a different license if that seems necessary.
The Artistic Licence covers only modifications to the original source code. Because your file is an addition, not a modification, you are free to license it as you please.
If you're not interested in the provisions of the Artistic License (e.g. people documenting their changes) then it would make sense to use a different license, or alternatively you could just release it into the public domain. But it's your file and you're free to do what you want with it.
