tests/test-backwards-remove.t

drawdag: don't crash when writing copy info to changesets

When writing copies to the changeset, localrepo.commitctx() will call
ctx.p1copies() and ctx.p2copies(). These crashed on simplecommitctx
because they ended up trying to access the manifest. drawdag doesn't
support copies at all, so we can simply override the methods to return
empty dicts.

Differential Revision: https://phab.mercurial-scm.org/D6565

  $ 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