title: Pandas: select all dates with specific month and day
body: <p>I have a dataframe full of dates and I would like to select all dates where the month==12 and the day==25 and add replace the zero in the <code>xmas</code> column with a 1.</p>
  
  <p>Anyway to do this? the second line of my code errors out.      </p>
  
  <pre><code>df = DataFrame({'date':[datetime(2013,1,1).date() + timedelta(days=i) for i in range(0,365*2)], 'xmas':np.zeros(365*2)})
  
  df[df['date'].month==12 and df['date'].day==25] = 1
  </code></pre>