Stricter jshint

Hey there,

I've set two other jshint options that I really like. One is more cosmetic ([unused](http://www.jshint.com/docs/options/#unused)), as it simply prevents variables laying around that no one uses, but the other one ([undef](http://www.jshint.com/docs/options/#undef)) can help detecting leaks.

I've fixed the code to comply to these rules as well. Wasn't that much fortunately.