title: How to plot a pandas multiindex dataFrame with all xticks
body: <p>I have a pandas dataFrame like this:</p>
  
  <pre><code>                     content
  date                        
  2013-12-18 12:30:00        1
  2013-12-19 10:50:00        1
  2013-12-24 11:00:00        0
  2014-01-02 11:30:00        1
  2014-01-03 11:50:00        0
  2013-12-17 16:40:00       10
  2013-12-18 10:00:00        0
  2013-12-11 10:00:00        0
  2013-12-18 11:45:00        0
  2013-12-11 14:40:00        4
  2010-05-25 13:05:00        0
  2013-11-18 14:10:00        0
  2013-11-27 11:50:00        3
  2013-11-13 10:40:00        0
  2013-11-20 10:40:00        1
  2008-11-04 14:49:00        1
  2013-11-18 10:05:00        0
  2013-08-27 11:00:00        0
  2013-09-18 16:00:00        0
  2013-09-27 11:40:00        0
  </code></pre>
  
  <p>date being the index.
  I reduce the values to months using:</p>
  
  <pre><code>dataFrame = dataFrame.groupby([lambda x: x.year, lambda x: x.month]).agg([sum])
  </code></pre>
  
  <p>which outputs:</p>
  
  <pre><code>         content
               sum
  2006 3        66
       4        65
       5        48
       6        87
       7        37
       8        54
       9        73
       10       74
       11       53
       12       45
  2007 1        28
       2        40
       3        95
       4        63
       5        56
       6        66
       7        50
       8        49
       9        18
       10       28
  </code></pre>
  
  <p>Now when I plot this dataFrame, I want the x-axis show every month/year as a tick. I have tries setting xticks but it doesn't seem to work. How could this be achieved? This is my current plot using dataFrame.plot():</p>
  
  <p><img src="https://i.stack.imgur.com/PUapV.png" alt="enter image description here"></p>