ERR: handle category dtype in .query with engine=numexpr
#### Code Sample, a copy-pastable example if possible

```python
# Your code here
import pandas as pd
BANDS = ["{}AM".format(i) for i in range(0,10)]
df = pd.DataFrame({'Time': BANDS})
df.Time = df.Time.astype('category', ordered=True,  categories=BANDS)
df.query("Time >= '5AM'" )
```
#### Problem description

The query fails with a ValueError: unknown type object.

Since Time is an ordered categorical and the query should return df[df.Time >= '5AM']

#### Expected Output
	Time
5	5AM
6	6AM
7	7AM
8	8AM
9	9AM
#### Output of ``pd.show_versions()``

<details>
# Paste the output here pd.show_versions() here
INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.41-36.55.amzn1.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.19.2
nose: 1.3.7
pip: 9.0.1
setuptools: 27.2.0
Cython: 0.25.2
numpy: 1.11.3
scipy: 0.18.1
statsmodels: 0.6.1
xarray: None
IPython: 5.1.0
sphinx: 1.5.1
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2016.10
blosc: None
bottleneck: 1.2.0
tables: 3.3.0
numexpr: 2.6.1
matplotlib: 1.5.3
openpyxl: 2.4.1
xlrd: 1.0.0
xlwt: 1.2.0
xlsxwriter: 0.9.6
lxml: 3.7.2
bs4: 4.5.3
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.1.4
pymysql: None
psycopg2: 2.6.2 (dt dec pq3 ext lo64)
jinja2: 2.9.4
boto: 2.45.0
pandas_datareader: None
</details>
