title: fig.show() does not bring the figure up
body: <pre><code>import matplotlib.pyplot as plt
  plt.ion()
  fig = plt.figure()
  axe = fig.add_subplot(111)
  axe.plot(x,y,'b-')
  axe.plot(z,h,'r-')
  </code></pre>
  
  <p>Now, I can see 2 lines (blue and red) plotted on figure. But I accidentally close that figure window.</p>
  
  <p>when I issue command <code>fig.show(), or fig.draw()</code>, the figure will never show up again. How can I bring up my original figure without executing above commands again?
  Thanks in advance. </p>