title: Pandas read_csv expects wrong number of columns, with ragged csv file
body: <p>I have a csv file that has a few hundred rows and 26 columns, but the last few columns only have a value in a few rows and they are towards the middle or end of the file. When I try to read it in using read_csv() I get the following error. 
  "ValueError: Expecting 23 columns, got 26 in row 64"</p>
  
  <p>I can't see where to explicitly state the number of columns in the file, or how it determines how many columns it thinks the file should have. 
  The dump is below</p>
  
  <pre><code>In [3]:
  
  infile =open(easygui.fileopenbox(),"r")
  pledge = read_csv(infile,parse_dates='true')
  
  
  ---------------------------------------------------------------------------
  ValueError                                Traceback (most recent call last)
  &lt;ipython-input-3-b35e7a16b389&gt; in &lt;module&gt;()
        1 infile =open(easygui.fileopenbox(),"r")
        2 
  ----&gt; 3 pledge = read_csv(infile,parse_dates='true')
  
  
  C:\Python27\lib\site-packages\pandas-0.8.1-py2.7-win32.egg\pandas\io\parsers.pyc in read_csv(filepath_or_buffer, sep, dialect, header, index_col, names, skiprows, na_values, thousands, comment, parse_dates, keep_date_col, dayfirst, date_parser, nrows, iterator, chunksize, skip_footer, converters, verbose, delimiter, encoding, squeeze)
      234         kwds['delimiter'] = sep
      235 
  --&gt; 236     return _read(TextParser, filepath_or_buffer, kwds)
      237 
      238 @Appender(_read_table_doc)
  
  C:\Python27\lib\site-packages\pandas-0.8.1-py2.7-win32.egg\pandas\io\parsers.pyc in _read(cls, filepath_or_buffer, kwds)
      189         return parser
      190 
  --&gt; 191     return parser.get_chunk()
      192 
      193 @Appender(_read_csv_doc)
  
  C:\Python27\lib\site-packages\pandas-0.8.1-py2.7-win32.egg\pandas\io\parsers.pyc in get_chunk(self, rows)
      779             msg = ('Expecting %d columns, got %d in row %d' %
      780                    (col_len, zip_len, row_num))
  --&gt; 781             raise ValueError(msg)
      782 
      783         data = dict((k, v) for k, v in izip(self.columns, zipped_content))
  
  ValueError: Expecting 23 columns, got 26 in row 64
  </code></pre>