tests/test-empty.t

rust-cpython: add panicking version of borrow_mut() and use it

The original borrow_mut() is renamed to try_borrow_mut().

Since leak_immutable() no longer incref the borrow count, the caller should
know if the underlying value is borrowed or not. No Python world is involved.
That's why we can simply use the panicking borrow_mut().

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 ..