tests/test-empty.t

rust-dirstatemap: add `NonNormalEntries` class

This fix introduces the same encapsulation as the `copymap`. There is no easy
way of doing this any better for now.

`hg up -r null && time HGRCPATH= HGMODULEPOLICY=rust+c hg up tip` on Mozilla
Central, (not super recent, but it doesn't matter):

Before: 7:44,08 total
After: 1:03,23 total

Pretty brutal regression!

This is a graft on stable of cf1f8660e568

Differential Revision: https://phab.mercurial-scm.org/D8111

Create an empty repo:

  $ hg init a
  $ cd a

Try some commands:

  $ hg log
  $ hg grep wah
  [1]
  $ hg manifest
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 0 changesets with 0 changes to 0 files

Check the basic files created:

  $ ls .hg
  00changelog.i
  cache
  requires
  store
  wcache

Should be empty:

  $ ls .hg/store

Poke at a clone:

  $ cd ..
  $ hg clone a b
  updating to branch default
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd b
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 0 changesets with 0 changes to 0 files
  $ ls .hg
  00changelog.i
  hgrc
  requires
  store

Should be empty:

  $ ls .hg/store

  $ cd ..