Failed cleanup

[René J.V. Bertin]

> > MacPorts does not currently have any background processes; adding one would be a major change.
> 
> This would also only be useful if there were something else MacPorts could be doing at the same time in the foreground. I think it would be confusing to add some sort of vacuum process that continued running after the main port(1) process exited.

I don't agree. From what I understand, this process is done after each clean and thus also repeatedly during a multi-port upgrade.
The upgrade process could continue while the vacuum is taking place (at least until it needs to access the database), and I don't see what's confusing when a process that most users don't know (nor care) about keeps running. All they notice is that the port command terminates a bit earlier than before.

R.