After closing the window, the gadgets allocated using creategadget() must
be released.  freegadgets() is a simple call that will free all the
GadTools gadgets that it finds, beginning with the gadget whose pointer is
passed as an argument.

    void FreeGadgets( struct Gadget *gad );

The gad argument is a pointer to the first gadget to be freed.  It is safe
to call freegadgets() with a null gadget pointer, the function will then
return immediately.  Before calling FreeGadgets(), the application must
first either remove the gadgets or close the window.

When the gadget passed to freegadgets() is the first gadget in a linked
list, the function frees all the GadTools gadgets on the list without
patching pointers or trying to maintain the integrity of the list.  Any
non-GadTools gadgets found on the list will not be freed, hence the result
will not necessarily form a nice list since any intervening GadTools
gadgets will be gone.

See the section on "creating gadget lists" for more information on using
linked lists of gadgets.