Added bounds checks for Listbox.InsertBefore(). This stupid 32-bit Mac bug keeps Listbox.Delete() unchecked for now...
Made Listboxes non-editable in Mac OS X; also more TODOs.
Removed gListboxSelected; it was never being called anyway (only gListboxSelectedMulti is; Windows still uses selectedIndex() for Listbox because of differences in how multi-selection listboxes are handled there and Mac OS X never had this function written to begin with).