tests/test-archive-symlinks.t

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

#require symlink

  $ origdir=`pwd`

  $ hg init repo
  $ cd repo
  $ ln -s nothing dangling

avoid tar warnings about old timestamp

  $ hg ci -d '2000-01-01 00:00:00 +0000' -qAm 'add symlink'

  $ hg archive -t files ../archive
  $ hg archive -t tar -p tar ../archive.tar
  $ hg archive -t zip -p zip ../archive.zip

files

  $ cd "$origdir"
  $ cd archive
  $ readlink.py dangling
  dangling -> nothing

tar

  $ cd "$origdir"
  $ tar xf archive.tar
  $ cd tar
  $ readlink.py dangling
  dangling -> nothing

#if unziplinks
zip

  $ cd "$origdir"
  $ unzip archive.zip > /dev/null 2>&1
  $ cd zip
  $ readlink.py dangling
  dangling -> nothing
#endif

  $ cd ..