rust-utils: move the `filesystem_now` function to a util
This is going to be useful for an upcoming `hg update` fastpath.
$ cat > abortcommit.py <<EOF
> from mercurial import error
> def hook(**args):
> raise error.Abort(b"no commits allowed")
> def reposetup(ui, repo):
> repo.ui.setconfig(b"hooks", b"pretxncommit.nocommits", hook)
> EOF
$ abspath=`pwd`/abortcommit.py
$ cat <<EOF >> $HGRCPATH
> [extensions]
> mq =
> abortcommit = $abspath
> EOF
$ hg init foo
$ cd foo
$ echo foo > foo
$ hg add foo
mq may keep a reference to the repository so __del__ will not be
called and .hg/journal.dirstate will not be deleted:
$ hg ci -m foo
error: pretxncommit.nocommits hook failed: no commits allowed
transaction abort!
rollback completed
abort: no commits allowed
[255]
$ hg ci -m foo
error: pretxncommit.nocommits hook failed: no commits allowed
transaction abort!
rollback completed
abort: no commits allowed
[255]
$ cd ..