`unused` option lost after first call

Hey Alexander!

qHint.validateFile() alters the options argument you pass it, specifically it deletes the unused member, so, when I hint scrips in a loop, I loose that option after the first file. :confused: 

I’ve checked [the code](https://github.com/gyoshev/qhint/blob/master/qhint.js#L28) and what I found seems from aside as some kind of obscure dance: it seems to treat unused-variable errors in a special way. :open_mouth:

I couldn’t infere the reason for that special treatment and I’ve tried to eliminate it. And it worked. :smile_cat:

What do you think about all this? :blush: