title: Cannot convert dataframe column to 24-H format datetime
body: <p>I have a <code>timestamp</code> column in my dataframe which is originally a <code>str</code> type. Some sample values:</p>
  
  <pre><code>'6/13/2015 6:45:58 AM'
  '6/13/2015 7:00:37 PM'
  </code></pre>
  
  <p>I use the following code to convert this values into datetime with 24H format using this code:</p>
  
  <pre><code>df['timestampx'] = pd.to_datetime(df['timestamp'], format='%m/%d/%Y %H:%M:%S %p')
  </code></pre>
  
  <p>And, I obtain this result:</p>
  
  <pre><code>2015-06-13 06:45:58
  2015-06-13 07:00:37
  </code></pre>
  
  <p>That means, the dates are NOT converted with 24H format and I am also loosing the AM/PM info. Any help?</p>