tests/test-websub.t

dirstate-tree: Avoid BTreeMap double-lookup when inserting a dirstate entry

The child nodes of a given node in the tree-shaped dirstate are kept in a
`BTreeMap` where keys are file names as strings. Finding or inserting a value
in the map takes `O(log(n))` string comparisons, which adds up when constructing
the tree.

The `entry` API allows finding a "spot" in the map that may or may not be
occupied and then access that value or insert a new one without doing map
lookup again. However the current API is limited in that calling `entry`
requires an owned key (and so a memory allocation), even if it ends up not
being used in the case where the map already has a value with an equal key.

This is still a win, with 4% better end-to-end time for `hg status` measured
here with hyperfine:

```
Benchmark #1: ../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
  Time (mean ± σ):      1.337 s ±  0.018 s    [User: 892.9 ms, System: 437.5 ms]
  Range (min … max):    1.316 s …  1.373 s    10 runs

Benchmark #2: ./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
  Time (mean ± σ):      1.291 s ±  0.008 s    [User: 853.4 ms, System: 431.1 ms]
  Range (min … max):    1.283 s …  1.309 s    10 runs

Summary
  './hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1' ran
    1.04 ± 0.02 times faster than '../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1'
```

* ./hg is this revision
* ../hg2/hg is its parent
* $REPO is an old snapshot of mozilla-central

Differential Revision: https://phab.mercurial-scm.org/D10550

#require serve

  $ hg init test
  $ cd test

  $ cat > .hg/hgrc <<EOF
  > [extensions]
  > # this is only necessary to check that the mapping from
  > # interhg to websub works
  > interhg =
  > 
  > [websub]
  > issues = s|Issue(\d+)|<a href="http://bts.example.org/issue\1">Issue\1</a>|
  > tickets = s|ticket(\d+)|<a href="http://ticket.example.org/issue\1">Ticket\1</a>|i
  > 
  > [interhg]
  > # check that we maintain some interhg backwards compatibility...
  > # yes, 'x' is a weird delimiter...
  > markbugs = sxbugx<i class="\x">bug</i>x
  > problems = sxPROBLEMx<i class="\x">problem</i>xi
  > EOF

  $ touch foo
  $ hg add foo
  $ hg commit -d '1 0' -m 'Issue123: fixed the bug! Ticket456 and problem789 too'

  $ hg serve -n test -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log
  $ cat hg.pid >> $DAEMON_PIDS

log

  $ get-with-headers.py localhost:$HGPORT "rev/tip" | grep bts
  <div class="description"><a href="http://bts.example.org/issue123">Issue123</a>: fixed the <i class="x">bug</i>! <a href="http://ticket.example.org/issue456">Ticket456</a> and <i class="x">problem</i>789 too</div>
errors

  $ cat errors.log

  $ cd ..