tests/test-extra-filelog-entry.t

dirstate-item: change the internal storage and constructor value

This should be closer to what we do need and what we can actually reliably
record.

In practice it means that we abandon the prospect of storing much more refined
data for now. We don't have the necessary information nor code using it right
now. So it seems safer to just use a clearer version of what we had so far.

See the documentation changes for details.

Differential Revision: https://phab.mercurial-scm.org/D11557

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