CONTRIBUTING

similar: sort files not by object id but by path for stable result

Perhaps the original implementation would want to sort added/removed files
alphabetically, but actually it did sort fctx objects by memory location.

This patch removes the use of set()s in order to preserve the order of
added/removed files. addedfiles.remove() becomes quadratic, but its cost
appears not dominant. Anyway, the quadratic behavior will be eliminated by
the next patch.

Benchmark with 50k added/removed files, on tmpfs:

  $ mkdir src
  $ for n in `seq 0 49`; do
  >     mkdir `printf src/%02d $n`
  > done

  $ for n in `seq 0 49999`; do
  >     f=`printf src/%02d/%05d $(($n/1000)) $n`
  >     dd if=/dev/urandom of=$f bs=8k count=1 status=none
  > done

  $ hg ci -qAm 'add 50k files of random content'
  $ mv src dest

  $ hg addremove --dry-run --time -q

  original:   real 16.550 secs (user 15.000+0.000 sys 1.540+0.000)
  this patch: real 16.730 secs (user 15.280+0.000 sys 1.440+0.000)

Our full contribution guidelines are in our wiki, please see:

https://www.mercurial-scm.org/wiki/ContributingChanges

If you just want a checklist to follow, you can go straight to

https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist

If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).