Changed the operation for generate_radio_group() so that it operates in the same way as generate_select() and can take either a simple or an associative array.   This enables custom fields to be presented as radio buttons instead of as <select> elements if desired.   See SF Support Requests #489.

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/trunk@2822 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7