title: pandas sort with capital letters
body: <p>Running this code:</p>
  
  <pre><code>df = pd.DataFrame(['ADc','Abc','AEc'],columns = ['Test'],index=[0,1,2])
  df.sort(columns=['Test'],axis=0, ascending=False,inplace=True)
  </code></pre>
  
  <p>Returns a dataframe column ordered as: <code>[Abc, AEc, ADc]</code>. 
  ADc should be before AEc, what's going on?</p>