tests/testlib/crash_transaction_late.py

treemanifest: stop storing full path for each item in manifest._lazydirs

This information is obtainable, if needed, based on the lazydirs key (which is
the entry name) and the manifest's `dir()` method.

### Performance

This is actually both a memory and a performance improvement, but it's likely to
be a very small one in most situations. In the pathological repo I've been using
for testing other performance work I've done recently, this reduced the time for
a rebase operation (rebasing two commits across a public-phase change that
touches a sibling of one of my tracked directories where the common parent is
massive (>>10k entries)):

#### Before

```
  Time (mean ± σ):      4.059 s ±  0.121 s    [User: 0.9 ms, System: 0.6 ms]
  Range (min … max):    3.941 s …  4.352 s    10 runs
```

#### After

```
  Time (mean ± σ):      3.707 s ±  0.060 s    [User: 0.8 ms, System: 0.8 ms]
  Range (min … max):    3.648 s …  3.818 s    10 runs
```

Differential Revision: https://phab.mercurial-scm.org/D9553

# tiny extension to abort a transaction very late during test
#
# Copyright 2020 Pierre-Yves David <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

from mercurial import (
    error,
    transaction,
)


def abort(fp):
    raise error.Abort(b"This is a late abort")


def reposetup(ui, repo):

    transaction.postfinalizegenerators.add(b'late-abort')

    class LateAbortRepo(repo.__class__):
        def transaction(self, *args, **kwargs):
            tr = super(LateAbortRepo, self).transaction(*args, **kwargs)
            tr.addfilegenerator(
                b'late-abort', [b'late-abort'], abort, order=9999999
            )
            return tr

    repo.__class__ = LateAbortRepo