title: Drop from datetime index dataframe rows based in year month day from another dataframe
body: <p>I have one dataframe like the following:</p>
  
  <pre><code>                       A     
  2014-06-02 09:00:00   ...
  2014-06-02 10:00:00   ...
  2014-06-02 11:00:00   ...
  2014-06-02 12:00:00   ...
  
  2014-06-03 09:00:00   ...
  2014-06-03 10:00:00   ...
  
  2014-06-04 11:00:00   ...
  2014-06-04 12:00:00   ...
  
  2014-06-05 11:00:00   ...
  2014-06-05 12:00:00   ...
  </code></pre>
  
  <p>And another like the following</p>
  
  <pre><code>                       A
  2014-06-03 13:14:00   ...
  2014-06-04 16:33:00   ...
  </code></pre>
  
  <p>I need one dataframe like the following :</p>
  
  <pre><code>                       A
  2014-06-02 09:00:00   ...
  2014-06-02 10:00:00   ...
  2014-06-02 11:00:00   ...
  2014-06-02 12:00:00   ...
  2014-06-05 11:00:00   ...
  2014-06-05 12:00:00   ...
  </code></pre>
  
  <p>That is: Drop from the first dataframe every row having year-month-day in the second dataframe</p>