rust-matchers: fix quadratic complexity in `FileMatcher`
Concretely, this command:
```
$ echo hg up -r <nodeid>; time hg revert dir1 dir2 -r <othernode> --debug
hg up -r <nodeid>
real 0m14.690s
user 0m14.766s
sys 0m5.430s
```
was much slower despite using 16 cores before this change.
The approach taken here is the same one used in match.py, in exactmatcher.
This changeset was originally written by Valentin Gatien-Baron in a private
repository.
I have redacted the commit message and did a minor clean up of the code.
#require bzr
$ . "$TESTDIR/bzr-definitions"
$ cat > ghostcreator.py <<EOF
> import sys
> from breezy import workingtree
> import breezy.bzr.bzrdir
> wt = workingtree.WorkingTree.open('.')
>
> message, ghostrev = sys.argv[1:]
> wt.set_parent_ids(wt.get_parent_ids() + [ghostrev.encode()])
> wt.commit(message)
> EOF
ghost revisions
$ mkdir test-ghost-revisions
$ cd test-ghost-revisions
$ brz init -q source
$ cd source
$ echo content > somefile
$ brz add -q somefile
$ brz commit -q -m 'Initial layout setup'
$ echo morecontent >> somefile
$ "$PYTHON" ../../ghostcreator.py 'Commit with ghost revision' ghostrev
$ cd ..
$ hg convert source source-hg
initializing destination source-hg repository
scanning source...
sorting...
converting...
1 Initial layout setup
0 Commit with ghost revision
$ glog -R source-hg
o 1@source "Commit with ghost revision" files+: [], files-: [], files: [somefile]
|
o 0@source "Initial layout setup" files+: [somefile], files-: [], files: []
$ cd ..