[js] argument names are not escaped for reserved identifiers

[nadako]

@jcward found this one. shouldn't be too hard to fix:

class Main {
    static function main() {
        v(10);
    }

    static function v(isNaN) {
        trace(Math.isNaN(isNaN));
    }
}

Main.v = function(isNaN) {
	console.log(isNaN(isNaN));
};