Setting option 'display.max_seq_items' to None results in TypeError when pprinting index

According to the docstring, the following is allowed:

``` Python
pd.set_option('display.max_seq_items', None)
```

With 0.16.1 this results in a TypeError when pretty printing an index. This is because the None value is compared against lenght of the index to see if we need to limit output.

``` Python
TypeError: unorderable types: int() > NoneType()
```
