tests/test-backwards-remove.t

streamclone: abort when client needs to handle obsmarkers, but doesn't

When client doesn't have any of obsolescence markers exchange capabilities,
then it's safe to say it can't handle obsmarkers. However, if it understands
even one format version, then stream clones are fine -- client can use
"obsmarkers" bundle2 part.

  $ hg init
  $ echo This is file a1 > a
  $ hg add a
  $ hg commit -m "commit #0"
  $ ls
  a
  $ echo This is file b1 > b
  $ hg add b
  $ hg commit -m "commit #1"
  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

B should disappear

  $ ls
  a