Query function gives error if column names have front slash
```
import pandas
df = pandas.DataFrame({'ColName / WithFrontSlash': [1, 2]})
df['ColName / WithFrontSlash']

0    1
1    2
Name: ColName / WithFrontSlash, dtype: int64

#this output is what is exptected
```

```
df.query('ColName / WithFrontSlash > 1')
pandas.computation.ops.UndefinedVariableError: name 'ColName' is not defined
```

Pandas version is 0.17.1
