title: numpy.isnan(value) not the same as value == numpy.nan?
body: <p>Why am I getting the following:</p>
  
  <pre><code>&gt;&gt;&gt; v
  nan
  &gt;&gt;&gt; type(v)
  &lt;type 'numpy.float64'&gt;
  &gt;&gt;&gt; v == np.nan
  False
  &gt;&gt;&gt; np.isnan(v)
  True
  </code></pre>
  
  <p>I would have thought the two should be equivalent?</p>