[pca] PCA return codes

[Martin Paul]

Jeff A. Earickson wrote:
> This may be nitpicky, but I would reorder it as:
> 
>         0  No error
>         1  Unknown error
>         2  Usage error
>         3  Reboot recommended
>         4  Reboot required to continue patch installation
>         5  Reboot required
> 
> That way (errcode > 2) means "you should reboot" and (errcode > 3) means
> "you must reboot".

I had thought so at first, too, maybe order all exit codes by how 
critical they are. But then it occurred to me that there surely will be 
requests for new, extra exit codes in the future, and that there will be 
no way to keep them in such an order without resorting them all the time.

So it's clear from the beginning now that you will have to check for 
explicite codes in your wrapper (and not ">" or "<").

Martin.