allow custom labels for empty allowed value in non-required radio buttons and select fields

if i create a non-required text field configured as radio buttons or a select field and give it a list of allowed values like this:

si|Yes
|No
dunno|Maybe

what i end up seeing as the label for the blank value is "N/A" or "-None-", instead of "No"

this may look like #368771: Create Documentation about removing N/A option for not required radio buttons but i think it's a different and much smaller issue. just swapping the empty choice created in the optionwidgets module with the $options field fixes it: from

      $options = array('' => theme('optionwidgets_none', $field)) + $options;

to

      $options = $options + array('' => theme('optionwidgets_none', $field));