title: pandas dataframe to_csv works with sep='\n' but not sep='\t'
body: <p>I try to print my large dataframe to csv file but the tab separation <code>sep='\t'</code> does not work. I then test with newline <code>sep='\n'</code>, it seems work ok, break all the elements by newline. What are possibly wrong here?</p>
  
  <p>The code is so simple like</p>
  
  <pre><code>df_M.to_csv('report'+filename, header=True, sep='\t', index=False)
  </code></pre>
  
  <p>The example of data (the protein column is very long), I mark where to separate by <code>|</code></p>
  
  <pre><code>"protein |  cl      | pept |    [M] |  [M+1H+]1+ |  [M+2H+]2+"      
  "ALBU_HUMAN_UPS Serum albumin (Chain 26-609) - Homo sapiens (Human)|    0|   AWAVAR|        672.37072|            673.378| out-of-range"        
  "ALBU_HUMAN_UPS Serum albumin (Chain 26-609) - Homo sapiens (Human)|    0|  TPVSDR| 673.3394900000002|  674.3467700000002|  out-of-range"       
  "ALBU_HUMAN_UPS Serum albumin (Chain 26-609) - Homo sapiens (Human)|    0|  NYAEAK| 694.3285900000001|  695.3358700000001|  out-of-range"       
  "
  </code></pre>