ERROR: test_constructor_unsortable (pandas.tests.test_categorical.TestCategorical)
``` python
======================================================================
ERROR: test_constructor_unsortable (pandas.tests.test_categorical.TestCategorical)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/var/tmp/portage/dev-python/pandas-0.17.0/work/pandas-0.17.0-python3_4/lib/pandas/core/algorithms.py", line 198, in factorize
    sorter = uniques.argsort()
TypeError: unorderable types: datetime.datetime() > int()

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/tmp/portage/dev-python/pandas-0.17.0/work/pandas-0.17.0-python3_4/lib/pandas/core/categorical.py", line 265, in __init__
    codes, categories = factorize(values, sort=True)
  File "/var/tmp/portage/dev-python/pandas-0.17.0/work/pandas-0.17.0-python3_4/lib/pandas/core/algorithms.py", line 207, in factorize
    lambda x: isinstance(x,string_types) ]
  File "/var/tmp/portage/dev-python/pandas-0.17.0/work/pandas-0.17.0-python3_4/lib/pandas/core/algorithms.py", line 206, in <listcomp>
    np.sort(np.array([ e for i, e in enumerate(uniques) if f(e) ],dtype=object)) for f in [ lambda x: not isinstance(x,string_types),
  File "/usr/lib64/python3.4/site-packages/numpy/core/fromnumeric.py", line 819, in sort
    a.sort(axis, kind, order)
TypeError: unorderable types: datetime.datetime() > int()

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/tmp/portage/dev-python/pandas-0.17.0/work/pandas-0.17.0-python3_4/lib/pandas/tests/test_categorical.py", line 94, in test_constructor_unsortable
    Categorical.from_array(arr, ordered=True)
  File "/var/tmp/portage/dev-python/pandas-0.17.0/work/pandas-0.17.0-python3_4/lib/pandas/core/categorical.py", line 351, in from_array
    return Categorical(data, **kwargs)
  File "/var/tmp/portage/dev-python/pandas-0.17.0/work/pandas-0.17.0-python3_4/lib/pandas/core/categorical.py", line 271, in __init__
    raise TypeError("'values' is not ordered, please explicitly specify the "
TypeError: 'values' is not ordered, please explicitly specify the categories order by passing in a categories argument.

----------------------------------------------------------------------
Ran 9056 tests in 1000.617s
```

```
INSTALLED VERSIONS
------------------
commit: None
python: 3.4.3.final.0
python-bits: 64
OS: Linux
OS-release: 4.1.9-lh
machine: x86_64
processor: Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz
byteorder: little
LC_ALL: None
LANG: en_GB.utf8

pandas: 0.17.0
nose: 1.3.7
pip: 7.1.2
setuptools: 18.4
Cython: 0.23.4
numpy: 1.10.1
scipy: 0.16.0
statsmodels: 0.6.1
IPython: None
sphinx: 1.3.1
patsy: 0.4.0
dateutil: 2.4.2
pytz: 2015.6
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.4.4
matplotlib: 1.4.3
openpyxl: 2.2.6
xlrd: 0.9.4
xlwt: 1.0.0
xlsxwriter: 0.7.7
lxml: 3.4.4
bs4: 4.4.1
html5lib: 0.9999999
httplib2: 0.9.2
apiclient: None
sqlalchemy: 1.0.8
pymysql: 0.6.7.None
psycopg2: 2.6.1 (dt dec pq3 ext lo64)
```
