#1 FXListBox doesn't look like FXList

[Anonymous]

Please unify the FXList and FXListBox APIs to be more
consistent about FXListItem.

FXListBox doesn't expose FXListItems at all, but should
follow the same conventions that FXList does.

For example:
FXListItem *FXList::retrieveItem(FXint index) const {
versus
FXString FXListBox::retrieveItem(FXint index) const {