When a subcommand gives an error and ignore_errors is false, we die with the error output.  But when ignore_errors is true, there's no way to see the error output, even when running with -d.  This change fixes that but emitting the error output in debug mode.

I also changed the log messages a bit when running a command, to make it clear that we're running a subcommand.

(Note: for some reason, the diff doesn't apply cleanly, so if you click on the 'view diff' button you'll just get an error message.  But this is a small diff, so hopefully you can download the diff and apply the changes by hand, if you're interested in taking this change.)