Believed to be no longer needed as I've squashed the last ones.
Note that, in Test.Framework, I can see no reason for the code to have
run it twice. It does not cause running processes to exit after all,
so any process that has leaked and is running and causing problems with
cleanup of the directory won't be helped by running it.
This commit was sponsored by Mark Reidenbach on Patreon.
The only price paid is one additional MVar read per write to the journal.
Presumably writing a journal file dominiates over a MVar read time by
several orders of magnitude.
--batch does not get the speedup because then it needs to notice when
another process has made a change. Also made the assistant and other damon
modes bypass the optimisation, which would not help them anyway.