title: Remove duplicates in a tuple of tuples
body: <p>I have the following tuple of tuples:</p>
  <pre><code># my Noah's Ark    
  myanimals = (('cat', 'dog'), ('callitrix', 'platypus'), ('anaconda', 'python'), ('mouse', 'girafe'),   ... ,('platypus', 'callitrix'))
  </code></pre>
  <p>Since I want a unique list of 2-tuple of animals, the pair ('platypus', 'callitrix') is considered to be a duplicate of ('callitrix', 'platypus').</p>
  <p>How can I elegantly remove from myanimals (with the minimum of code) all the kind of pairs (b,a) duplicates of (a, b) ?</p>