DOC: Cookbook example on reading CSV by chunking gives error
URL linked in the cookbook: http://stackoverflow.com/questions/11622652/large-persistent-dataframe-in-pandas/12193309#12193309

Traceback:

``` python
  File "/usr/local/lib/python2.7/dist-packages/pandas/tools/merge.py", line 929, in concat
    verify_integrity=verify_integrity)
  File "/usr/local/lib/python2.7/dist-packages/pandas/tools/merge.py", line 944, in __init__
    '"{0}"'.format(type(objs).__name__))
AssertionError: first argument must be a list-like of pandas objects, you passed an object of type "TextFileReader"
```

To be precise: Concatenation does not work in this example.
