startupitem: add new option startupitem.logfile.stderr, for capturing stderr

[mascguy]

Presently, when startupitem.logfile is specified, we add a plist entry for stdout logging (via StandardOutPath). But when errors and such occur - particularly due to a fatal startup issue - that output often goes to stderr.

Not capturing the latter, makes troubleshooting more difficult for users. Potentially requiring them to manually edit the plist file, to add an entry for StandardErrorPath themselves.

To ensure the user doesn't have to deal with that, add new option startupitem.logfile.stderr.

By default, it is set to startupitem.logfile. But the user can specify a different logfile, clear the value (to disable stderr logging), or set it independently of startupitem.logfile (if only stderr should be logged).

Fixes: https://trac.macports.org/ticket/67955

[jmroot]

I would like a separate option to control where stderr is sent. That can default to the same log as stdout.

[mascguy]

I would like a separate option to control where stderr is sent. That can default to the same log as stdout.

How about this:

• Add new option startupitem.logfile.stderr
• Defaults to startupitem.logfile
• If cleared, disables stderr logging
• Can be set independently of startupitem.logfile, if user only wants stderr logging

[mascguy]

PR updated to support new option startupitem.logfile.stderr, along with update to the manpage.

Note: Once we have consensus for all of the details, a corresponding PR will be created to update the MacPorts Guide.