rem: WMSetMenuItemEnabled(WMGetFromArray(bPtr->items, index), flag);
add: WMSetMenuItemEnabled(WMGetFromArray(bPtr->items, index), (flag ? 1 : 0));
context: WMSetPopUpButtonItemEnabled(WMPopUpButton *bPtr, int index, Bool flag){    WMSetMenuItemEnabled(WMGetFromArray(bPtr->items, index), flag);}