obsolete: introduce caches for all meaningful sets This changeset introduces caches on the `obsstore` that keeps track of sets of revisions meaningful for obsolescence related logics. For now they are: - obsolete: changesets used as precursors (and not public), - extinct: obsolete changesets with osbolete descendants only, - unstable: non obsolete changesets with obsolete ancestors. The cache is accessed using the `getobscache(repo, '<set-name>')` function which builds the cache on demand. The `clearobscaches(repo)` function takes care of clearing the caches if any. Caches are cleared when one of these events happens: - a new marker is added, - a new changeset is added, - some changesets are made public, - some public changesets are demoted to draft or secret. Declaration of more sets is made easy because we will have to handle at least two other "troubles" (latecomer and conflicting). Caches are now used by revset and changectx. It is usually not much more expensive to compute the whole set than to check the property of a few elements. The performance boost is welcome in case we apply obsolescence logic on a lot of revisions. This makes the feature usable!

http://mercurial.selenic.com/bts/issue1175

  $ hg init
  $ touch a
  $ hg ci -Am0
  adding a

  $ hg mv a a1
  $ hg ci -m1

  $ hg co 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg mv a a2
  $ hg up
  note: possible conflict - a was renamed multiple times to:
   a2
   a1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg ci -m2

  $ touch a
  $ hg ci -Am3
  adding a

  $ hg mv a b
  $ hg ci -Am4 a

  $ hg ci --debug --traceback -Am5 b
  b
   b: searching for copy revision for a
   b: copy a:b80de5d138758541c5f05265ad144ab9fa86d1db
  committed changeset 5:89e8e4be0de296fa3d6dd7825ccc44d7dc0f1f3b

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  4 files, 6 changesets, 4 total revisions

  $ hg export --git tip
  # HG changeset patch
  # User test
  # Date 0 0
  # Node ID 89e8e4be0de296fa3d6dd7825ccc44d7dc0f1f3b
  # Parent  7fc86ba705e717a721dbc361bf8c9bc05a18ca2f
  5
  
  diff --git a/b b/b
  new file mode 100644