(update_frame_tool_bar): Update code for GNUStep.
(clearAll): New method.
(addDisplayItemWithImage:idx:tag:helpText:enabled:): Handle new tag
- argument. Call insertItemWithItemIdentifier when NS_IMPL_GNUSTEP.
+ argument. Call insertItemWithItemIdentifier when NS_IMPL_GNUSTEP.
Move identifierToItem setObject and activeIdentifiers addObject before
call to insertItemWithItemIdentifier.
(validateVisibleItems): Fix indentation.