'This will be called if button 3 is clicked.  This will remove
a label if not in inline mode.  Unfortunately, if one is doing
inline labels, then there is currently no way to fix the
broken contour - once humpty-dumpty is broken, he can\'t be put
back together.  In inline mode, this does nothing.'

def button3(self, event):

    if self.inline:
        pass
    else:
        self.cs.pop_label()
        self.cs.ax.figure.canvas.draw()
