Fix arg handling for org-contents

Fix arg handling for org-contents

When odd levels are being used, change the interpretation of a
numerical arg to S-TAB.

Michael Brand writes:

> I like the org-indent-mode with the soft-indentation but even more I
> like the hard-indentation with `#+STARTUP: odd hidestars' instead for
> which I have a question.
>
> This is the content of the example file oddeven:
> -*- mode: org -*-
> #+STARTUP: oddeven hidestars content
> * 1 Org Mode
> ** 1.1 Introduction
> *** 1.1.1 Installation
>
> This is the content of the example file odd:
> -*- mode: org -*-
> #+STARTUP: odd hidestars content
> * 1 Org Mode
> *** 1.1 Introduction
> ***** 1.1.1 Installation
>
> The different _Emacs-faces_ (colors) for the heading levels are the same
> when comparing the two files. This Emacs-internal adaptation I
> appreciate a lot.
>
> C-u 2 S-Tab shows _two_ levels with the file oddeven but only _one_ with
> the file odd. Is this how it is intended to work for the file odd?