title: Datetime does not work in my index series
body: <p>I have a hf5 filled with some data. </p>
  
  <p>when I open it in python I have this output</p>
  
  <pre><code>hf['SB'].head()
  
  0_1                     price   cng     
  2015-07-15 07:30:00.087 12.61   4
  2015-07-15 07:30:00.087 12.61   1
  2015-07-15 07:30:00.087 12.61   1
  2015-07-15 07:30:00.087 12.61   2
  2015-07-15 07:30:00.087 12.61   19
  </code></pre>
  
  <p>This file ranges from 2015 to 2016.</p>
  
  <pre><code>hf['SB'].index
  
  DatetimeIndex(['2015-07-15 07:30:00.087000', '2015-07-15 07:30:00.087000',
                 '2015-07-15 07:30:00.087000', '2015-07-15 07:30:00.087000',
                 '2015-07-15 07:30:00.087000', '2015-07-15 07:30:00.087000',
                 '2015-07-15 07:30:00.087000', '2015-07-15 07:30:00.087000',
                 '2015-07-15 07:30:00.087000', '2015-07-15 07:30:00.087000',
                 ...
                 '2016-07-14 16:59:57.670000', '2016-07-14 16:59:58.047000',
                 '2016-07-14 16:59:59.170000', '2016-07-14 16:59:59.170000',
                 '2016-07-14 16:59:59.170000', '2016-07-14 16:59:59.170000',
                 '2016-07-14 16:59:59.170000', '2016-07-14 16:59:59.170000',
                 '2016-07-14 16:59:59.170000', '2016-07-14 16:59:59.957000'],
                dtype='datetime64[ns]', name=u'0_1', length=3961015, freq=None)
  </code></pre>
  
  <p>Well... My problem is:</p>
  
  <p>when I want a slice, for example, august 20 2015:</p>
  
  <pre><code>hf['SB'][datetime(2015,8,20)]
  </code></pre>
  
  <p>I got this error: <code>KeyError: datetime.datetime(2015, 8, 20, 0, 0)</code></p>
  
  <p>But if I use:</p>
  
  <pre><code>hf['SB']['2015-08-20']
  </code></pre>
  
  <p>its works!!!</p>
  
  <p>There is something wrong in my index file or I'm using <code>datetime</code> function wrong?</p>