tests/test-dirstate-backup.t

context: handle stringified ints in revsymbol()

This patch copies the handling of stringified ints from changectx's
constructor. It then calls repo.__getitem__ with the int. Since that
method only interprets integers as revnums the first thing it does,
this will not be redoing any of the work already done. We leave the
old code in place so we can later deprecate it instead of breaking
extensions.

Differential Revision: https://phab.mercurial-scm.org/D3146

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