title: Clip an image using several patches in matplotlib
body: <p>I have a plot in pylab which I want to clip to the borders of a map of the UK. </p>
  
  <p>I've also made a series of patches which contain the outlines of each country: one for England, one for Wales etc.</p>
  
  <p>Clipping the plot one patch works brilliantly:</p>
  
  <pre><code>fig = plt.figure()
  ax = fig.add_subplot(111)
  im = ax.scatter(x,y,c = z)
  ax.add_patch(patch)
  im.set_clip_path(patch)
  </code></pre>
  
  <p>But if I try and do it for more than one, it leaves me with nothing - understandably, since no part of the plot is within each country simultaneously. </p>
  
  <p>Does anyone know how I can clip using an 'OR' type statement? (ie. don't clip if within this patch or this one etc). </p>