transaction: allow finalizer to add finalizer
It will make some code (persistent nodemap related) simpler to write, because
higher level code can blindly queue finalization without thinking too hard about
the context.
Differential Revision: https://phab.mercurial-scm.org/D7833
#require clang-format test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "$TESTDIR"/..
$ for f in `testrepohg files 'set:(**.c or **.cc or **.h) and not "listfile:contrib/clang-format-ignorelist"'` ; do
> clang-format --style file $f > $f.formatted
> cmp $f $f.formatted || diff -u $f $f.formatted
> rm $f.formatted
> done