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This is a good idea! thanks happy melon :-)
What about if someone was say to create a user group called for example Print, that would conflict with Mediawiki:Print.css, We could perhaps prefix the page names with something like [[Mediawiki:Group-<group>]].
Prefixing sounds like a good idea.
This can be said for most possible words, where conflict may be possible (granted, less likely, but possible)
Also, you've added a new code file, and then just listed Roan and Trevor as the author :)
I'm really, really bad at copying license headers and getting other random stuff as well; it generally doesn't get very rigorous review... :D I think I copied the class description from Skin.php to an extension once...
Just for the record:
Does not take an extra http-request (nice!)