title: Adding one month to datetime64 with timedelta
body: <p>When I try this:</p>
  
  <pre><code>&gt;&gt;&gt; a = numpy.datetime64('1995-12-31')
  &gt;&gt;&gt; b = a + pandas.Timedelta(1, unit='M')
  &gt;&gt;&gt; print(b)
  </code></pre>
  
  <p>I expect to see </p>
  
  <pre><code>1996-01-31
  </code></pre>
  
  <p>but instead I get </p>
  
  <pre><code>1996-01-30 10:29:06.
  </code></pre>
  
  <p>Any idea why? Many thanks. </p>