Series.loc/iloc[x, y] does not raise exception
#### Code Sample, a copy-pastable example if possible

```
df = pd.DataFrame({'a': [10]})
# df['a'] is a series, can be indexed with 1 index only

# will raise IndexingError, as expected
df['a'].iloc[0, 0]
df['a'].loc[0, 0]

# will raise nothing, not as expected
df['a'].iloc[0, 0] = 1000 # equivalent to pass
df['a'].loc[0, 0] = 1000 # equivalent to df['a'].loc[0] = 1000

```

See [this SO post](http://stackoverflow.com/a/38644472/336527)
#### Expected Output

Expected an IndexingError exception in every case where two values are used to index a Series.
#### output of `pd.show_versions()`

pandas version 0.18.1, python 3.5
