title: Error using pandas.ExcelWriter.to_excel in python-3.3
body: <p>I'm using Pandas version 0.16.2 and openpyxl version 2.2.4 in python-3.3. I am trying to write a pretty simple pandas dataframe containing floats, strings and NaNs. When I use the code:</p>
  
  <pre><code>import pandas as pd
  writer = pd.ExcelWriter(xls_path)
  df.to_excel(writer,'sheet1')
  writer.save()
  </code></pre>
  
  <p>I get the error:</p>
  
  <pre><code>TypeError                                 Traceback (most recent call last)
  
  &lt;ipython-input-3-2349bf9de8ec&gt; in save_xls(list_dfs, xls_path, sheetnames)
        5                  import pandas as pd
        6                  writer = pd.ExcelWriter(xls_path)
  ----&gt; 7             df.to_excel(writer,sheetnames[n])
        8 
        9     writer.save()
  
  /Users/dylan/Virtualenvs/ve33/lib/python3.3/site-packages/pandas/core/frame.py in to_excel(self,     excel_writer, sheet_name, na_rep, float_format, columns, header, index, index_label, startrow,     startcol, engine, merge_cells, encoding, inf_rep)
     1272         formatted_cells = formatter.get_formatted_cells()
     1273         excel_writer.write_cells(formatted_cells, sheet_name,
  -&gt; 1274                                  startrow=startrow, startcol=startcol)
     1275         if need_save:
     1276             excel_writer.save()
  
  /Users/dylan/Virtualenvs/ve33/lib/python3.3/site-packages/pandas/io/excel.py in write_cells(self,     cells, sheet_name, startrow, startcol)
      776 
      777             if style_kwargs:
  --&gt; 778                 xcell.style = xcell.style.copy(**style_kwargs)
      779 
      780             if cell.mergestart is not None and cell.mergeend is not None:
  
  /Users/dylan/Virtualenvs/ve33/lib/python3.3/site-packages/openpyxl/compat/__init__.py in     new_func(*args, **kwargs)
       65                 lineno=_code.co_firstlineno + 1
       66             )
  ---&gt; 67             return obj(*args, **kwargs)
       68         return new_func
       69 
  
  TypeError: copy() got an unexpected keyword argument 'font'    
  </code></pre>
  
  <p>Any help on what could be going wrong?</p>
  
  <p>Thanks!</p>