KeyError: 'version' on import
I'm running pandas 0.17.1 on Python 2.7.10 on RHEL 7.12, and I am experiencing the following behavior:

```
In [1]: import pandas
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-1-d6ac987968b6> in <module>()
----> 1 import pandas

/var/lib/jenkins/jobs/Test-Client/workspace/venv/lib/python2.7/site-packages/pandas/__init__.py in <module>()
     60 # use the closest tagged version if possible
     61 import pdb; pdb.set_trace()
---> 62 from ._version import get_versions
     63 v = get_versions()
     64 __version__ = v.get('closest-tag',v['version'])

KeyError: 'version'
```

This appears with both Python and IPython. I've inserted a debugger into the `__init__` script and examined what get_versions returns at that time. It looks like this:

```
(Pdb) v
{u'e\x00r\x00r': None, u'f\x00u\x00l\x00l\x00-\x00r\x00e\x00v': u'6\x00c\x003\x000\x00c\x00b\x00e\x00c\x00f\x008\x00e\x005\x00a\x00e\x006\x001\x000\x00f\x002\x00a\x00', u'd\x00i\x00r': False, u'v\x00e\x00r\x00s': u'0\x00.\x001\x00'}
```

`get_versions()` just calls json.loads on a `version_json` dictionary in the `_version` file (generated by the versioneer). The `version_json` dictionary appears fine at time of import, however:

```
(Pdb) version_json
'\n{\n "dirty": false,\n "error": null,\n "full-revisionid": "6c30cbecf8e5ae610f2a37ba821116bd9f77044d",\n "version": "0.17.1"\n}\n'
```

It looks like the ultrajson library included with pandas works differently for me on the server than my local development machine. Both have ultrajson version 1.33.

I should also note that when I try to rerun `import pandas` in the same REPL, I get a different error:

```
In [2]: import pandas
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-2-d6ac987968b6> in <module>()
----> 1 import pandas

/var/lib/jenkins/jobs/Test-Client/workspace/venv/lib/python2.7/site-packages/pandas/__init__.py in <module>()
     11                       "pandas from the source directory, you may need to run "
     12                       "'python setup.py build_ext --inplace' to build the C "
---> 13                       "extensions first.".format(module))
     14 
     15 from datetime import datetime

ImportError: C extension: hashtable not built. If you want to import pandas from the source directory, you may need to run 'python setup.py build_ext --inplace' to build the C extensions first.
```

Thanks,
Sam
