tests/test-dirstate-backup.t

narrow: drop server support for widening using the getbundle command (BC)

The client still supports widening using the getbundle, which we
(Google) still depend on a for a little while more (we've started the
migration to the new narrow_widen command, but we're not done yet).

Differential Revision: https://phab.mercurial-scm.org/D7093

Set up

  $ hg init repo
  $ cd repo

Try to import an empty patch

  $ hg import --no-commit - <<EOF
  > EOF
  applying patch from stdin
  abort: stdin: no diffs found
  [255]

No dirstate backups are left behind

  $ ls .hg/dirstate* | sort
  .hg/dirstate