BUG: categorical doesn't handle display.width of None in Python 3 (GH10087)
closes #10087

I think this is fairly straightforward, however I am not sure if the prior code comparing `display.width` to 0 was correct... is `display.width` ever supposed to be set to 0? It looks suspiciously similar to a snippet from `Series.__unicode__()`, but that is looking at `display.max_rows`. Maybe it was brought over incorrectly?

If it should just be a simple comparison to None, not 0 as it was before, just let me know and I'll amend this.
