P.S.: Spin button inside a menu item

[Nix <nix go-nix ca>]

One way that works some of the time is to give the menu to a
GtkOptionMenu.  Then, the following sequence of events takes place:

Click on the option menu
- the menu pops up

Select the spin button menu item
Move the mouse into the spin button and try clicking
Doesn't work
- the menu item closes, and now the GtkOptionMenu displays it as
the selected menu item

Click on the option menu
- the menu pops up

Select the spin button menu item
Move the mouse into the spin button
- lo and behold, exactly what I want does happen

Unfortunately, it is not with a GtkOptionMenu that I would like to
see my menu item work, but on its own.  This, unfortunately, I cannot
get working :o(