'Add a button with a given title, the tab-next button,
its name in the Control table, giving its x position; the
y-position is aligned with the other buttons.
Return the button, so that events can be associated'

def xbutton(self, name, title, next, xpos):

    return self.pushbutton(name, int(((self.w * xpos) - 28)), (self.h - 27), 56, 17, 3, title, next)
