[PATCH setup] Propagate exit code of elevated process

[Ken Brown]

On 7/7/2018 8:40 AM, Jon Turney wrote:
> Propagate the exit code of elevated process, when --wait is used.
> 
> This addresses part of the problem about exit code noted in [1], although we
> also need to audit that a non-zero exit code is reported in all error
> situations.

I haven't done a complete audit, but I did happen to spot one place that 
needs attention.  See the comment (made by you in 2010) in 
PostInstallResultsPage::OnUnattended().

Ken