yesno( "text"[, $w_popover]), noyes()
Opens a toplevel widget and prompts the user for yes or no.
It returns 1, if the user clicked the Yes button. The function
yesno() has 0 as the default, noyes() has 1 as default.
Th optional parameter w_popover specifies the
position of the widget.
e.g.:
Util::yesno( "Do you really want it");