[#33184] Prevent using 'menu' as menutype as this is reserved for back-end menus

http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33184&start=0

patch will display an error if attempting to save such a menu type:
"Please change the Menu type. The term 'menu' is reserved for back-end usage."