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.

I think my git skills have gone rusty. I am trying to amend my commit, but it doesn't like that I have already pushed it - it won't accept my new (amended) push, saying I am behind the remote counterpart. But the remote just has the changes before the amended commit. Any hints?
 I just forced the push. Not sure if there was any better way.

At any rate, I incorporated most of your comment. I think 0 is a valid value, as it's checked against in code below. Thanks for your feedback!
 @rosnfeld Yes, you need to force if you amend a commit.
 Ok, good to know - thanks.

@jreback Travis is happy if you're happy (with this change).
 @rosnfeld thanks! hope this exercised those git skills! maybe need another PR to work on that :)
