Allow shapes to be set prior to toplevels being fully allocated

[dkfellows]

From the CAVEATS:

When setting the shape of a toplevel window, make sure that you perform an update idletasks between the creation of the toplevel and applying a shape set or shape update operation to it. This is because Tk works by reparenting toplevel windows into a (user-invisible) container, so allowing the introduction of a menubar to windows without having to alter the internal dimensions of the toplevel. Because this is done on an idle handler, you must wait until after that idle handler has executed before applying a reshape operation to a toplevel. Failure to do this will result in the reshaped toplevel being apparently encased in a toplevel window that is unresponsive to all events (like <Expose> events). While no harm is done to the application, this an undesirable effect that you probably do not want in your application.

This needs addressing.