End measuring on an axis.

def _onLeftButtonUp(self, evt):
        """End measuring on an axis."""
        x = evt.GetX()
        y = self.figure.bbox.height - evt.GetY()
        #print 'release button', 1
        evt.Skip()
        if self.HasCapture(): self.ReleaseMouse()
        FigureCanvasBase.button_release_event(self, x, y, 1, guiEvent=evt)