pandas.io.tests.test_parsers.Test*.test_yy_format fails in 0.18.0
#### Code Sample, a copy-pastable example if possible

```
$ nosetests-2.7 pandas.io.tests.test_parsers:TestCParserHighMemory.test_yy_format
F
======================================================================
FAIL: test_yy_format (pandas.io.tests.test_parsers.TestCParserHighMemory)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/pandas/io/tests/test_parsers.py", line 1064, in test_yy_format
    tm.assert_frame_equal(rs, xp)
  File "/usr/local/lib/python2.7/site-packages/pandas/util/testing.py", line 1097, in assert_frame_equal
    obj='{0}.index'.format(obj))
  File "/usr/local/lib/python2.7/site-packages/pandas/util/testing.py", line 729, in assert_index_equal
    obj=obj, lobj=left, robj=right)
  File "pandas/src/testing.pyx", line 58, in pandas._testing.assert_almost_equal (pandas/src/testing.c:3809)
  File "pandas/src/testing.pyx", line 147, in pandas._testing.assert_almost_equal (pandas/src/testing.c:2685)
  File "/usr/local/lib/python2.7/site-packages/pandas/util/testing.py", line 880, in raise_assert_detail
    raise AssertionError(msg)
AssertionError: DataFrame.index are different

DataFrame.index values are different (100.0 %)
[left]:  DatetimeIndex(['2031-09-01 00:10:00', '2028-09-02 10:20:00',
               '2031-09-03 08:30:00'],
              dtype='datetime64[ns]', name=u'date_time', freq=None)
[right]: DatetimeIndex(['2009-01-31 00:10:00', '2009-02-28 10:20:00',
               '2009-03-31 08:30:00'],
              dtype='datetime64[ns]', name=u'date_time', freq=None)

----------------------------------------------------------------------
Ran 1 test in 0.085s

FAILED (failures=1)
```

Also `pandas.io.tests.test_parsers:TestCParserLowMemory.test_yy_format` and `pandas.io.tests.test_parsers:TestPythonParser.test_yy_format`.

This appears to be in the class of bugs described in #3341.

```
$ python
Python 2.7.11 (default, Jan  9 2016, 17:23:07)
[GCC 4.2.1 Compatible FreeBSD Clang 3.4.1 (tags/RELEASE_34/dot1-final 208032)] on freebsd10
Type "help", "copyright", "credits" or "license" for more information.
>>> import dateutil.parser
>>> p = dateutil.parser.parser()
>>> p.parse('090131', dayfirst=False, yearfirst=False)
datetime.datetime(2031, 9, 1, 0, 0)
>>> p.parse('090131', dayfirst=False, yearfirst=True)
datetime.datetime(2009, 1, 31, 0, 0)
>>> p.parse('090131', dayfirst=True, yearfirst=False)
datetime.datetime(2031, 1, 9, 0, 0)
>>> p.parse('090131', dayfirst=True, yearfirst=True)
datetime.datetime(2009, 1, 31, 0, 0)
>>>
```
#### Expected Output

Expect tests to pass.
#### output of `pd.show_versions()`

This is reproducible with both of the following configurations.

```
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.11.final.0
python-bits: 64
OS: FreeBSD
OS-release: 10.2-STABLE
machine: amd64
processor: amd64
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.18.0
nose: 1.3.7
pip: 8.0.2
setuptools: 20.0
Cython: None
numpy: 1.10.4
scipy: 0.16.1
statsmodels: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.5.0
pytz: 2015.7
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.5
matplotlib: 1.5.0
openpyxl: 2.3.3
xlrd: 0.9.3
xlwt: 0.7.5
xlsxwriter: 0.8.4
lxml: 3.5.0
bs4: 4.4.1
html5lib: 0.9999999
httplib2: None
apiclient: None
sqlalchemy: 0.7.10
pymysql: None
psycopg2: None
jinja2: 2.8
boto: 2.38.0
```

```
INSTALLED VERSIONS
------------------
commit: None
python: 3.4.4.final.0
python-bits: 64
OS: FreeBSD
OS-release: 10.2-STABLE
machine: amd64
processor: amd64
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.18.0
nose: 1.3.7
pip: None
setuptools: 20.0
Cython: 0.23.4
numpy: 1.10.4
scipy: 0.16.1
statsmodels: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.5.0
pytz: 2015.7
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.5
matplotlib: None
openpyxl: 2.3.3
xlrd: 0.9.3
xlwt: None
xlsxwriter: 0.8.4
lxml: 3.5.0
bs4: 4.4.1
html5lib: 0.9999999
httplib2: None
apiclient: None
sqlalchemy: 0.7.10
pymysql: None
psycopg2: None
jinja2: 2.8
boto: 2.38.0
```
