transaction: clarify the logic around pre-finalize/post-finalize
I am taking a bit more verbose route, but I find it easier to follow for people
who (re)discover the code.
(This is a gratuitous cleanup I did while looking at something else.)
Differential Revision: https://phab.mercurial-scm.org/D8176
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state