tests/test-revert-unknown.t

revlog: add attribute on revlogs that specifies its kind

The sidedata logic needs to check whether the revlog it's working on is a
changelog, a manifest or a filelog.
Furthermore, future versions of the revlog format will most likely see a split
between the three types (i.e. they will store different information), so having
this will be useful for other future endeavors as well.

Differential Revision: https://phab.mercurial-scm.org/D10151

  $ hg init
  $ touch unknown

  $ touch a
  $ hg add a
  $ hg ci -m "1"

  $ touch b
  $ hg add b
  $ hg ci -m "2"

Should show unknown

  $ hg status
  ? unknown
  $ hg revert -r 0 --all
  removing b

Should show unknown and b removed

  $ hg status
  R b
  ? unknown

Should show a and unknown

  $ ls -A
  .hg
  a
  unknown