Optimise jQuery.fn.add by removing redundant makeArray call

* Don't pass a plain array to makeArray
In case of a node, the array is obviously an array already as it is created right there on the same line.

* Don't pass an object to both makeArray and jQuery.merge
The selector can be an array or array-like object here (e.g. NodeList/jQuery etc.). In that case jQuery.merge already takes care of turning it into an array, no need to do apply first (in fact, makeArray calls jQuery.merge internally).