title: np.timedelta64 does not accept np.int64
body: <p>Why does np.timedelta64 does not accept numpy integers such as np.int64?</p>
  
  <pre><code>np.timedelta64(np.int64(2),'h')
  
  ---------------------------------------------------------------------------
  ValueError                                Traceback (most recent call last)
  &lt;ipython-input-75-fd40c0d8eac0&gt; in &lt;module&gt;()
  ----&gt; 1 np.timedelta64(np.int64(2),'h')
  
  ValueError: Could not convert object to NumPy timedelta
  </code></pre>