tests/test-extra-filelog-entry.t

typing: add trivial type hints to `mercurial.scmutil`

There's still a lot to go, but there's a lot here already, so I tried to keep it
to obvious/trivial things.  I didn't bother with contexts, matchers, and
revisions that can be `bytes | int | None`.

Issue351: mq: qrefresh can create extra revlog entry

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "mq=" >> $HGRCPATH

  $ hg init repo
  $ cd repo
  $ hg qinit

  $ echo b > b
  $ hg ci -A -m foo
  adding b

  $ echo cc > b
  $ hg qnew -f foo.diff
  $ echo b > b
  $ hg qrefresh

  $ hg debugindex b
     rev linkrev       nodeid    p1-nodeid    p2-nodeid
       0       0 1e88685f5dde 000000000000 000000000000