.iloc[:] and .loc[:] return the original object
Each of these asserts should fail:

``` python
# on pandas 0.18.1
import pandas as pd

df = pd.DataFrame({'x': range(3)})
assert df.iloc[:] is df
assert df.loc[:] is df

series = df.x
assert series.iloc[:] is series
assert series.loc[:] is series
```

Instead, for the sake of predictability, these should always return a new DataFrame/Series, even if they reuse the same data. See [here](https://github.com/pydata/pandas/issues/13842#issuecomment-236685599) for an example of how this resulted in a user facing bug within pandas.

Thanks @mborysow for pointing this out.
