[pca] PCA return codes

[Christophe Kalt]

On Sep 16, Fred Chagnon wrote:
| In my wrapper script for pca, I would like to be able to determine if pca
| finished patching completely, or if it finished prematurely, perhaps due to
| a patch that required an immediate reconfigure reboot. Does pca have
| different return codes for these situations? Where can I see a list of
| possible exit situations?

Agreed, suggested it back in February as it's part of what
makes it painful to write a decent wrapper around pca.