Opens a dialog that presents a binary choice to the user. The user is forced to choose between these two options, ie cancelling or closing the dialog opens a message box asking the user to actually choose one of the two options.
The dialog will contain the string message and two buttons, labeled with the true-choice and the false-choice. If the user clicks on true-choice #t is returned. If the user clicks on false-choice, #f is returned.
The argument default-result determines how closing the window is treated. If the argument is 'disallow-close, closing the window is not allowed. If it is anything else, that value is returned when the user closes the window.