"certificate verify failed" errors on macports
Sorry for this sketch of a bug report, but I am seeing these errors with Macports Python 2.7 and the current pandas 0.15.2 release:

https://travis-ci.org/MacPython/scipy-stack-osx-testing/jobs/47389975#L757

Here's an example error:

```
======================================================================
ERROR: test_url (pandas.io.tests.test_json.test_pandas.TestPandasContainer)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pandas/util/testing.py", line 1441, in wrapper
    return t(*args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pandas/io/tests/test_json/test_pandas.py", line 599, in test_url
    result = read_json(url, convert_dates=True)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pandas/io/json.py", line 174, in read_json
    filepath_or_buffer, _ = get_filepath_or_buffer(path_or_buf)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pandas/io/common.py", line 118, in get_filepath_or_buffer
    req = _urlopen(str(filepath_or_buffer))
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 154, in urlopen
    return opener.open(url, data, timeout)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 431, in open
    response = self._open(req, data)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 449, in _open
    '_open', req)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 409, in _call_chain
    result = func(*args)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 1240, in https_open
    context=self._context)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 1197, in do_open
    raise URLError(err)
URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:581)>
```

No such errors for Python 3:

https://travis-ci.org/MacPython/scipy-stack-osx-testing/jobs/47389977

Is this a bug in Macports Python or Pandas?
