Unable to import Stata 13 database files with read_stata()
pandas v0.14.0 (May 31 , 2014) seems uncapable of importing Stata 13 datasets although according to this http://pandas.pydata.org/pandas-docs/stable/whatsnew.html, it should. Stata 12 files can be imported without problems.

The output of running this

``` python
import pandas
pandas.show_versions()
dta = pandas.io.stata.read_stata('D:\\Datos\\rferrer\\Desktop\\myauto.dta')
```

follows:

``` python
%run D:/Datos/RFERRER/Desktop/import_stata13.py

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.6.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 45 Stepping 7, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.14.0
nose: 1.3.0
Cython: 0.19.2
numpy: 1.8.0
scipy: 0.14.0
statsmodels: 0.5.0
IPython: 1.2.1
sphinx: 1.2.2
patsy: 0.2.0
scikits.timeseries: 0.91.3
dateutil: 2.2
pytz: 2013.8
bottleneck: None
tables: 2.4.0
numexpr: 2.2.2
matplotlib: 1.3.1
openpyxl: 1.8.5
xlrd: 0.9.2
xlwt: 0.7.5
xlsxwriter: None
lxml: 3.2.3
bs4: None
html5lib: 0.95-dev
bq: None
apiclient: None
rpy2: None
sqlalchemy: 0.8.3
pymysql: None
psycopg2: None
C:\Users\rferrer\AppData\Local\Enthought\Canopy\User\lib\site-packages\openpyxl\__init__.py:31: UserWarning: The installed version of lxml is too old to be used with openpyxl
  warnings.warn("The installed version of lxml is too old to be used with openpyxl")
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
C:\Users\rferrer\AppData\Local\Enthought\Canopy\App\appdata\canopy-1.4.0.1938.win-x86_64\lib\site-packages\IPython\utils\py3compat.pyc in execfile(fname, glob, loc)
    195             else:
    196                 filename = fname
--> 197             exec compile(scripttext, filename, 'exec') in glob, loc
    198     else:
    199         def execfile(fname, *where):

D:\Datos\RFERRER\Desktop\import_stata13.py in <module>()
      3 pandas.show_versions()
      4 
----> 5 dta = pandas.io.stata.read_stata('D:\\Datos\\rferrer\\Desktop\\myauto.dta')

C:\Users\rferrer\AppData\Local\Enthought\Canopy\User\lib\site-packages\pandas\io\stata.pyc in read_stata(filepath_or_buffer, convert_dates, convert_categoricals, encoding, index)
     45         identifier of column that should be used as index of the DataFrame
     46     """
---> 47     reader = StataReader(filepath_or_buffer, encoding)
     48 
     49     return reader.data(convert_dates, convert_categoricals, index)

C:\Users\rferrer\AppData\Local\Enthought\Canopy\User\lib\site-packages\pandas\io\stata.pyc in __init__(self, path_or_buf, encoding)
    455             self.path_or_buf = path_or_buf
    456 
--> 457         self._read_header()
    458 
    459     def _read_header(self):

C:\Users\rferrer\AppData\Local\Enthought\Canopy\User\lib\site-packages\pandas\io\stata.pyc in _read_header(self)
    657 
    658         """Calculate size of a data record."""
--> 659         self.col_sizes = lmap(lambda x: self._calcsize(x), self.typlist)
    660 
    661     def _calcsize(self, fmt):

C:\Users\rferrer\AppData\Local\Enthought\Canopy\User\lib\site-packages\pandas\io\stata.pyc in <lambda>(x)
    657 
    658         """Calculate size of a data record."""
--> 659         self.col_sizes = lmap(lambda x: self._calcsize(x), self.typlist)
    660 
    661     def _calcsize(self, fmt):

C:\Users\rferrer\AppData\Local\Enthought\Canopy\User\lib\site-packages\pandas\io\stata.pyc in _calcsize(self, fmt)
    661     def _calcsize(self, fmt):
    662         return (type(fmt) is int and fmt
--> 663                 or struct.calcsize(self.byteorder + fmt))
    664 
    665     def _col_size(self, k=None):

TypeError: cannot concatenate 'str' and 'NoneType' objects
```

The dataset `myauto.dta` is just the `auto` dataset made available running `sysuse auto` within Stata.

The problem is originally documented here: http://stackoverflow.com/questions/24053652/pandas-and-stata-13-files.

My Python is set up with [Enthough Canopy 1.4.0 (64 bit)](https://www.enthought.com/products/canopy/).
