Fixed missing autocomplete after content filter was removed.

I assume that #filter [name=field] was confused with either #has-defined
[name=field] or #field-is [name=field] or both and somehow change() wasn't
doing anything.
Dropped the name attribute again in #has-defined etc.

I cannot live in a world where I would explicitely address the only <select>
tag in a form. So I've made the script look stupid in only one place instead.
Replaced $.add() with the comma selector.
Replaced $.first() with the :first selector.