tests/test-merge8.t

clfilter: introduce `filteredrevs` attribute on changelog

This changeset allows changelog object to be "filtered". You can assign a set of
revision numbers to the `changelog.filteredrevs` attributes. The changelog will
then pretends these revision does not exists in this repo.

A few methods need to be altered to achieve this behavior:

- tip
- __iter_
- irevs
- hasnode
- headrevs

For consistency and to help debugging, the following methods are altered too.
Tests tend to show it's not necessary to alter them but have them raise proper
exception helps to detect bad acces to filtered revisions.

- rev
- node
- linkrev
- parentrevs
- flags

The following methods would also need alteration for consistency purpose but
this is non-trivial and not done yet.

- nodemap
- strip

The C version of headrevs is not run if there is any revision to filter. It'll
need a proper rewrite later to restore performance.

Test for changeset ba7c74081861
(update dirstate correctly for non-branchmerge updates)
  $ hg init a
  $ cd a
  $ echo a > a
  $ hg add a
  $ hg commit -m a
  $ cd ..
  $ hg clone a b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd a
  $ hg mv a b
  $ hg commit -m move
  $ echo b >> b
  $ hg commit -m b
  $ cd ../b
  $ hg pull ../a
  pulling from ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 1 files
  (run 'hg update' to get a working copy)
  $ hg update
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ cd ..