tests/test-dirstate-backup.t

tests: make autodiff.py work on Python 3

This patch adds b'' to string literal to make it compatible with in-core Python
3 compatibility.

# skip-blame because we are just adding b''

Differential Revision: https://phab.mercurial-scm.org/D1791

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