tests/test-extra-filelog-entry.t

docs: prefer `hg diff --from/--to` over `-r`

This patch includes updating away from the broken `hg diff -r
'date(...)'` (see not in previous patch).

Differential Revision: https://phab.mercurial-scm.org/D9555

Issue351: mq: qrefresh can create extra revlog entry

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

  $ hg init
  $ 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           p2
       0       0 1e88685f5dde 000000000000 000000000000